sphere of radius ‘3a’ with its - kvjhunjhunu.orgkvjhunjhunu.org/QBphysics.pdf · In parallel plate capacitor, ... A parallel plate capacitor with air as dielectric is connected

Very short Answer type Questions [1 mark each]

1. Why must electrostatic field at the surface of a charged conductor be normal to the surface at every point? Give reason.

2. What is meant by the statement that the electric field of a point charge has spherical symmetry whereas that of an electric dipole is cylindrically symmetric?

3. Two charges of magnitudes – 2Q and + Q are located at points (a, 0) and (4a, 0) respectively. What is the electric flux due to this charge through a sphere of radius ‘3a’ with its center at the origin?

4. Why do the electric field lines never cross each other? 5. Define electric dipole moment. Is it scalar or vector? 6. An electric dipole is placed, in a uniform electric field. What is net force

acting on it? 7. How does the force between two point charges change if the dielectric

constant of the medium in which they are kept increase? 8. Under what conditions, the electric lines of force are straight? 9. Why do the electrostatic field lines not form closed loops?

10. Draw an equipotential surface in a uniform electric field. 11. The given graph shows the variation of charge 'Q' versus potential

difference 'V' for capacitors C1 and C2. The two capacitors have the same plate separation, but the plate area of C2 is double that of C1, which of the lines in the graph correspond to C1 and C2 and why?

Q A

B

V

12. When kept in an electric field, does a proton move from lower to higher potential or from higher to lower potential?

13. In a medium, the force of attraction between two point electric charges, distance d apart is F. What distance apart should these be kept in the same medium so that the force between them becomes (i) 3 F (ii) F/ 3?

14. A metallic sphere is charged negatively. Will its mass increase, decrease or remain the same? 15. Give three differences between the nature of electric potentials of a single

point charge and an electric dipole. 16. The potential energy of an electric dipole placed in a uniform electric field is

zero. What is the orientation of vector P and vector E ? 17. In parallel plate capacitor, the capacitance increases from 4μF to 80 μF, on

introducing a dielectric medium between the plates. What is the dielectric constant of the medium?

18. An electric dipole of dipole moment 20 X106 C m. It is enclosed by a closed surface. What is the net electric flux coming out of surface?

19. What is the amount of work done in moving a 100 μc charge between two points 5 cm apart on an equipotential surface?

Very short Answer type Questions [2 marks each] 20. Although ordinary rubber is insulator, the rubber tyres of air craft are made

slightly conducting. Why? 21. Figure shows three charges + 2q, -q and + 3q. Two charges +2q and –q are

enclosed within a surface ‘S’. What is the electric flux due to this

configuration through the surface ‘S’?

22. A system has two charges qA = 2.5 × 10–7 C and qB = –2.5 × 10–7 C located at points A: (0, 0, –15 cm) and B: (0,0, +15 cm), respectively. What are the total charge and electric dipole moment of the system?

23. How much work is required in turning an electric dipole of dipole moment p- >

from its position of stable equilibrium to its position of unstable equilibrium in a uniform electrostatic field?

24. Two fixed point charges +4e and +e units are separated by a distance 'a'. Where should the third point charge be placed for it to be in equilibrium?

25. A point charge of 1.8 μC is at the center of a cubical Gaussian surface having each side 50 cm. What is the net electric flux through the surface?

26. Electric field intensity in a given region is zero. Can we conclude that electric potential must be zero?

27. What is the work done in moving a 2μC point charge from corner A to corner

B of square ABCD. When a 10 μC charge exists at the center of the square?

Short Answer Type Questions-II [3 marks each]

28. Define electric flux. Write its S.I. units. A spherical rubber balloon carries a charge that is uniformly distributed over its surface. As the balloon is blown up and increases in size, how does the total electric flux coming out of the surface change? Give reason.

29. Derive the expression for the energy stored in a parallel plate capacitor

with air between the plates. How does the stored energy change if air is

replaced by a medium of dielectric constant K?

30. A parallel plate capacitor with air as dielectric is connected to a power supply and charged to a potential difference Vo. After disconnecting from power supply, a sheet of insulating material is inserted between the plates completely filling the space between them. What will be the effect on (i) charge on the plates (ii) electric field between the plates (iii) potential difference between the plates (iv) capacitance (v) energy stored in the capacitor.

31. An electric dipole consists of two opposite charges of magnitude 1μC each

and is separated by a distance of 3 cm. The dipole is placed in an electric field of 4 × 105 N/C. Find the maximum torque on the dipole.

32. A slab of material of dielectric constant K has the same area as that of the

plates of a parallel plate capacitor but has the thickness d/2, where d is the separation between the plates. Find out the expression for its capacitance when the slab is inserted between the plates of the capacitor.

33. A parallel plate capacitor, each of plate area A and separation ‘d’ between

the two plates, is charge with charges + Q and – Q on the two plates. Deduce the expression for the energy stored in the capacitor.

34. State Gauss’s theorem. Apply this theorem to obtain an expression for the electric field intensity at a point due to an infinitely long uniformly charged straight wire.

35. Define electric field intensity. Write its S.I. unit. Write the magnitude and

direction of electric field intensity due to an electric dipole of length 2a at the mid-point of the line joining the two charges

36. An electric dipole with moment P is placed in a uniform electric field E .

Write the expression for the torque experienced by the dipole. Identify two parts of perpendicular vectors in the expression. Show diagrammatically the orientation of the dipole in the field for which the torque is (i) maximum (ii) half the maximum value (iii) zero.

37. Derive an expression for electric potential due to an electric dipole at any

point on its axis. Mention the contrasting feature of electric potential of a dipole at a point as compared to that due to a single charge.

38. A slab of material of dielectric constant K has the same area as that of the

plates of a parallel plate capacitor but has the thickness 2d/3, where d is the separation between the plates. Find out the expression for its capacitance when the slab is inserted between the plates of the capacitor.

39. An oil drop of 12 excess electrons is held stationary under a constant electric

field of 2.55x104 N/C. Estimate the radius of the drop. (density of oil = 1.26 g cm-3,g=9.81 ms-2 and e= 1.6x10-19C).

Long Answer Type Questions [5 marks each]

40 (a)Deduce an expression for the capacitance of a parallel plate capacitor with air as the medium between the plates (b)A dielectric slab of thickness ‘t’ is kept in between the plates each of area A of parallel plate capacitor separated by a distance of ‘d’. Drive an expression for the capacitance of capacitor for t <<d.

40 (b) Using Gauss law, derive an expression for the electric field intensity at

any point outside a uniformly charged thin spherical shell of radius R and charge density σ C/m- 2 Draw the field lines when the charge density of the sphere is (i) positive, (ii) negative. (b) A uniformly charged conducting sphere of 2m in diameter has a surface charge density of 100μC/m -2. Calculate the (i) charge on the sphere (ii) total electric flux passing through the sphere.

41. Define the term electric dipole moment. Give its unit. Derive an expression for

the maximum torque acting on the electric dipole when held in uniform electric field. In which orientation, a dipole placed in a uniform electric field is in (i) stable, (ii) unstable equilibrium?

42. Derive an expression for the torque experienced by an electric dipole kept

in a uniformly electric field. 43. Two charged particles, having equal charges of 2.0 × 10-5 C each, are

brought from infinity to within a separation of 10 cm. Find the increase in the electric potential energy during the process.

44. The electric field components due to a charge inside the cube of side 0.1m

Are as shown:

Ex= x where NmC-1 Calculate (i) the flux through the cube and (ii) the charge inside the cube.

45. Use Gauss’s law to obtain an expression for the electric field due to an

infinitely long straight uniformly charged wire.

.

46. Electric field in the above figure is directed along + X direction and given by Ex = 5Ax + 2B, where E is in NC-1 and x is in metre, A and B are constants

with dimensions. Talking A=10N/C/m and B = 5N/C calculate. (i) the electric flux through the cube. (ii) net charge enclosed within the cube.

47. An electric dipole with moment P is placed in a uniform electric field E .

Write the expression for the torque experienced by the dipole. Identify two parts of perpendicular vectors in the expression. Show diagrammatically the orientation of the dipole in the field for which the torque is (i) maximum (ii) half the maximum value (iii) zero.

48. (i) explain briefly how a capacitor stores energy on charging. Obtain

expression for energy stored. (ii) A parallel plate capacitor of plate separation’s’ is charged to a p.d. ‘V’. A

dielectric slab of thickness d and dielectric constant K is introduced between the plates while the battery remains connected to the plates.

(a) Find the ratio of energy stored in the capacitor after and before the dielectric in introduced, give physical explanation for this charge in stored energy.

(b) What happens to the charge on the capacitor? (c) How does the electric field between plates change. ********************************************************************************************************

Very short Answer type Questions [1 mark each] 1. Name the quantity that can be found from the slope of the graph of Current

density’ j’ and drift velocity ‘Vd ‘of the charge carriers.

2. Two identical cells, each of emf E, having negligible internal resistance, are connected in parallel with each other across an external resistance R. What is the current through this resistance?

3. Two materials, Ag and GaAs, are cooled from 300 K to 60 K. What will be

the effect on the resistivity?

4. Why are the connecting resistors in a meter bridge made of thick copper strips?

5. Define the term ‘drift velocity’ of charge carriers in a conductor and write its relationship with the current flowing through it.

6. Sketch a graph showing variation of resistivity of carbon with temperature.

7. Explain how the average velocity of free electrons in a metal at constant

temperature, in an electric field, remains constant even though the electrons are

being constantly accelerated by this electric field?

8. Why potentiometer is preferred over voltmeter for measuring emf.

9. What is meant by the sensitivity of a potentiometer?

Very short Answer type Questions [2 marks each]

10. The V-I graphs of two resistors, and their series combination, are

shown in the adjoining figure. Which one of these graphs represents the series combination of the other two? Give reasons for your answer.

11. Name the two factors on which the resistivity of a given material

depends. A carbon resistor has a value of 62K with a tolerance of 5%. Give

the colour code for this resistor.

12. V-I graph for a metallic wire at two different temperatures T1 and T2 is as shown in the following figure. Which of the two temperatures is higher and why?

13. The V-I graphs of two resistors of the same material and the same radii

with lengths L1 and L2 are shown in fig. If L1 > L2, state with reason which of these graphs represents voltage – current change for L1.

14. A cell of emf 2 V and internal resistance 0.1 Ω is connected to a 3.9 Ω

external resistance. What will be the p.d. across the terminals of the cell?

15. A potential difference V is applied to a conductor of length L. How is the drift velocity affected when V is doubled and L is halved?

16. A cell of 6 V and internal resistance 2Ω is connected to a variable

resistor. For what value of current does maximum power dissipation occur in the circuit?

17. The plot of the variation of potential difference across a combination of three identical cells in series, versus current is as shown below. What is the emf of each cell?

18. The resistance of the platinum wire of a platinum resistance thermometer at the ice point is 5Ω and at steam point is 5.23Ω. When the thermometer is inserted in a hot bath, the resistance of the platinum wire is 5.795Ω. Calculate the temperature of the bath.

19. A cell of emf (E) and internal resistance (r) is connected across a variable external resistance (R). Plot graphs to show variation of (i) E with R, (ii) Terminal p.d. of the cell (V) with R.

20. Find the value of the unknown resistance X in the circuit if no current flows through the galvanometer. Assume the resistance per unit length of the wire is 0.01Ωcm-1.

21. Given n resistors each of resistance R, how will you combine them to get the (i) maximum (ii) minimum effective resistance? What is the ratio of the maximum to minimum resistance?

22. Draw V-I graph for ohmic and non- ohmic materials. Give one example

for each.

23. In a potentiometer arrangement, a cell of emf 1.25 V gives a balance

point at 35.0cm length of the wire. If the cell is replaced by another cell

and the balance point shifts to 63.0cm, what is the emf of the second cell?

Is the balance point affected by the internal resistance of the driver cell?

Short Answer Type Questions-II [3 marks each] 24. In the potentiometer circuit shown, the balance point is at X. State with

reason where the balance point will be shifted when (i)Resistance R is increased, keeping all parameters unchanged. (ii)Resistance S is increased keeping R constant.

(iii)Cell P is replaced by another cell whose emf is lower than that of that cell

Q.

25 .A potentiometer wire of length 1.0 m has a resistance of 15 Ω. It is connected to a 5 V battery in series with a resistance of 5 Ω. Determine the emf of the primary cell which gives a balance point at 60 cm.

26. When two identical cells E and internal resistance r each are connected in series with a resistor R = 10, a current of 0.75 A flows in the circuit. Just one cell across the same R, however, sends a current of 0.50 A. Find the emf and internal resistance of the cell.

27. Describe briefly, with the help of a circuit diagram, how a potentiometer is

used to determine the internal resistance of a cell. 28. Explain the term ‘drift velocity’ of electrons in a conductor. Hence obtain the

expression for the current through a conductor in terms of ‘drift velocity’.

29. Answer the following:

(a) Why are the connections between the resistors in a meter bridge made of thick copper strips? (b) Why is it generally preferred to obtain the balance point in the middle of the meter bridge wire? (c) Which material is used for the meter bridge wire and why?

30.E2 =1.02V, PQ=1m.When switch S open, null position is obtained at a distance of 51 cm from P. Calculate (i) potential gradient (ii) emf of the cell E1 (iii) when switch S is closed, will null point move towards P or Q. Give reason for your answer

31. Using data given in graph determine (i) emf (ii) internal resistance of the cell. (iii) For what current, does maximum power dissipation occur in the

circuit?

32. In a meter bridge the null point is found at a distance of 33.7cm from A, when resistance R is connected in left gap and S is connected in the right gap. If now a resistance of 12Ω is connected in parallel with S, the null point occurs at 51.9cm. Determine the values of R and S.

33. Two students X and Y perform an experiment on potentiometer separately using the circuit keeping other things unchanged (i) X increases the value of distance R. (ii) Y decreases the value of resistance S in the set up. How would these changes affect the position of null point in each case and

why?

34.How does the drift speed of the electrons change through a metal wire if (a) potential difference is increased. (b) temperature is increased. (c) metal wire is stretched.

35.Two wires of equal length, one of aluminum and the other of copper have the same resistance. Which of the two wires is lighter? Hence explain why aluminum wires are preferred for overhead power cables.(ρAl=2.63X10 -8Ωm,

ρCu=1.72 X 10-8 Ωm, Relative density of Al= 2.7, of Cu = 8.9)

36.A potentiometer wire of length 100cm has a resistance of 10Ω is connected in

series with a resistance and cell of emf 2V of negligible internal resistance. A

source of emf of 10mV is balanced against a length of 40cm of potentiometer

wire. What is the value of the external resistance?

37. In a potentiometer circuit of a battery of negligible internal resistance is set

up as shown to develop a constant potential gradient along the wire AB.

Two cells of emf E1 and E2 are connected in series as shown in the

combination (1) and (2). The balance points are obtained respectively at

400cm and 240cm from the point A. Find (i) E1/ E2 and (ii) balancing length

for the cell E1 only.


38. State the principle of potentiometer. Draw a circuit diagram to show the use of potentiometer to compare the emf of two primary cells. Write the formula used. How can the sensitivity of a potentiometer be increased.

39. Are the paths of electrons straight lines, between successive collisions, in the (i) absence of electric field (ii) presence of electric field. Establish a relation between drift velocity and current. Hence obtain the relation between current density and drift velocity.

40. Deduce the condition for balance in a Wheatstone bridge. Using the principle of Wheatstone bridge, describe the method to determine the specific resistance of a wire in the laboratory. Draw the circuit diagram and write the formula used. Write any two precautions.

********************************************************************************************************

G E1 E2

E1 E2

Very short Answer type Questions [1 mark each] 1. What is the direction of the force acting on a charge particle q, moving with a

velocity v in a uniform magnetic field B? 2. Define one tesla using the expression for the magnetic force acting on a

particle of charge ‘q’ moving with velocity v in a magnetic field B 3. How will the magnetic field at the center of a circular coil carrying current change if

the current through the coil is double and the radius of the coil is halved?

4. Magnetic field lines can be entirely confined within the core of a toroid, but not within a straight solenoid. Why?

5. An electron does not suffer any deflection while passing through a region of uniform magnetic field. What is the direction of the magnetic field?

6. A beam of a particles projected along +x-axis, experiences a force due to a magnetic field along the +y-axis. What is the direction of the magnetic field?

7. Mention the two characteristic properties of the material suitable for making core of a transformer.

8. An electron is moving along positive x- axis in the presence of uniform

magnetic field along positive y -axis. What is the direction of the force acting

on it?

9. Where on the surface of the earth is the vertical component of earth’s magnetic field zero?

10. Steel is preferred for making permanent magnets whereas soft iron is

preferred for making electromagnets .Give one reason.

11. A narrow beam of protons and deuterons, each having the same momentum, enters a region of uniform magnetic field directed perpendicular to their direction of momentum. What would be the ratio of the circular paths described by them?

12. Why should the spring or suspension wire in a moving coil galvanometer

have low torsional constant?

13. Where on the surface of Earth is the angle of dip zero? 14. The permeability of a magnetic material is 0.9983. Name the type of magnetic

materials it represents.


15. An electron and a proton moving with the same speed enter the same magnetic field region at right angles to the direction of the field. Show the trajectory followed by the two particles in the magnetic field. Find the ratio of the radii of the circular paths which the particles may describe.

16. The vertical component of Earth’s magnetic field at a place is 3 times the horizontal component. What is the value of angle of dip at this place?

17. Two current carrying loops carrying current I each and radii r each are place

coaxially such that their centers are separated by a distance r. If the current

flowing in the coils are in same sense as observed by an observer from one

side then find the magnitude of magnetic field at the mid point of the line

joining their centers.

18. Define the term magnetic dipole moment of a current loop. Write the expression for the magnetic moment when an electron revolves at a speed ‘v’, around an orbit of radius ‘r’ in hydrogen atom.

19. Define magnetic susceptibility of a material. Name two elements, one having positive susceptibility and the other having negative susceptibility. What does negative susceptibility signify?

20. Draw magnetic field lines when a (i) diamagnetic, (ii) paramagnetic substance is placed in an external magnetic field. Which magnetic property distinguishes this behaviour of the field lines due to the two substances?

21. How can a galvanometer be converted into a voltmeter to read a maximum potential difference V? Discuss with related mathematical expression.

22. How will you convert a galvanometer into an ammeter of range 0 - I amperes? What is the effective resistance of an ammeter?

23. When a magnetic needle placed inside a uniform magnetic field a torque developed on it, give the condition of most stable and most unstable position of magnetic needle in the magnetic field.

24. State the factors on which the force acting on a charge moving in a magnetic field depends. Write the expression for this force. When is this force minimum and maximum?

Short Answer Type Questions-II [3 marks each] 25. A long straight wire of a circular cross-section of radius ‘a’ carries a steady

current ‘I’. The current is uniformly distributed across the cross-section.

Apply Ampere’s circuital law to calculate the magnetic field at a point ‘r’ in

the region for (i) r < a and (ii) r > a.

26. Define current sensitivity and voltage sensitivity of a galvanometer.

Increasing the current sensitivity may not necessarily increase the voltage

sensitivity of a galvanometer. Justify.

27. Explain how an atom behaves as a magnetic dipole. Derive an expression for

the magnetic dipole moment of the atom. Also define Bohr magneton.

28. A steady current (I1) flows through a long straight wire. Another wire

carrying steady current (I2) in the same direction is kept close and parallel to

the first wire. Show with the help of a diagram how the magnetic field due to

the current I1 exerts a magnetic force on the second wire. Write the

expression for this force.

29. Define the terms (i) magnetizing field, (ii) magnetic intensity, (iii)relative

permeability and (iv) magnetic susceptibility. Give their S I unit, if any

30. A long solenoid with closely wound turns has n turns per unit of its length. A steady current I flows through this solenoid. Use Ampere’s circuital law to obtain an expression for the magnetic field at a point on its axis and close to its mid point.

31. Define current sensitivity and voltage sensitivity of a galvanometer. State the factors on which the sensitivity of a moving coil galvanometer depends.

Long Answer Type Questions [5 marks each] 32. Derive a mathematical expression for the force per unit length acting on each

of the two straight parallel metallic conductors carrying current in the same direction and kept near each other. Hence define an ampere. Why do such current carrying conductors attract each other?

33. With the help of a neat and labeled diagram, explain the underlying principle, construction and working of a moving coil galvanometer. What is the function of (i) uniform radial field (ii) soft iron core in such a device?

34. Derive an expression for the torque on a rectangular coil of area A, carrying a current I and placed in a magnetic field B. The angle between the direction of B and vector perpendicular to the plane of the coil is .

35. State the principle of a cyclotron. Draw labeled diagram. Explain briefly how it works and how it is used to accelerate the charged particles. Show that the time period of ions in a cyclotron is independent of both the speed and radius of circular path.

36. What is resonance condition? How is it used to accelerate the charged particles? (i) Explain the use of electric field &magnetic field. (ii) Electron cannot be accelerated, why ?

37. Discuss the motion of a charged particle in a uniform magnetic field with

initial velocity (i) parallel to the field, (ii) perpendicular to the magnetic field

and (iii) at an arbitrary angle with the field direction.

38. Using Biot-Savart law, deduce an expression for the magnetic field on the axis

of a circular current loop. Hence obtain the expression for the magnetic field

at the center of the loop.


1. Define the term “watt-less current”.

2. What is the function of a step down transformer?

3. The peak value of emf in a.c. in E0. Write its (i) rms and (ii) average

value over a complete cycle.

4. What is the power dissipated in an a.c. circuit in which voltage and

current are given by V=230 sin (ωt+π/3) and I = 10 sin ωt?

5. A bulb and a capacitor are connected in series to an a.c. source of

variable frequency. How will the brightness of the bulb change on

increasing the frequency of the a.c. Source? Give reasons.

6. Two identical loops, one of copper and another of constantan are

removed from a magnetic field within the same time interval. In which

loop will the induced current be greater?

7. The power factor of an a.c. circuit is 0.5. What will be the phase

difference between voltage and current in this circuit?

8. In a series LCR circuit, the voltage across an inductor, capacitor and

resistor are 20V, 20V and 40V respectively. What is the phase difference

between the applied voltage and the current in the circuit?

9. When current in a coil changes with time, how is the back emf induced in the coil related to it?

10. The instantaneous current and voltage of an a.c. circuit are given by i =

10 sin (314 t) A and V = 50 sin (314t + π/2) V. What is the power of

dissipation in the circuit?

11. Define self-inductance. Give its S.I. units.

12. A rectangular loop of wire is pulled to the right, away from the long

straight wire through which a steady current I flows upwards. What

is the direction of induced current in the loop?


13. Two loops of different shapes are moved in a region of uniform

magnetic field in the directions marked by arrows as shown in the

figure. What is the direction of the induced current in each loop?

14. Two bar magnets are quickly moved towards a metallic loop

connected across a capacitor ‘C’ as shown in figure. Predict the

polarity of the capacitor.

15. The current flowing through a pure inductor of inductance 4mH is

I = 12 cos (300t) ampere. What is the (i) rms (ii) average value of

current for a complete cycle?

16. A closed loop PQRS of wire is moved into a uniform magnetic field at

right angles to the plane of the paper as shown in the figure. Predict

the direction of induced current in the loop.

17. A bar magnet is moved in the direction indicated by the arrow

between two coils PQ and CD. Predict the directions of induced

current in each coil.

18. Predict the direction of induced current in metal rings 1 and 2 when

current I in the wire is steadily decreasing?

19. Predict the direction of induced current in a metal ring when the ring is

moved towards a straight conductor with constant speed v. the

conductor is carrying current I in the direction shown in the figure.

20. How does the mutual inductance between two coils change when (i) distance between the coils is increased and (ii) number of turns in the coils is increased? 21. Draw the graphs showing the variations of (i) inductive reactance, and

(ii) capacitive reactance, with frequency of applied voltages in a.c.

circuit.

22. A perfect self-inductor when connected to an a.c. source does not

produce heating effect yet reduces the current in the circuit. Explain.

23. Prove that an ideal capacitor, in an a.c. circuit does not dissipate power.

24. Derive an expression for the self-inductance of a long air-cored solenoid

of length l and number of turns N.

25. (i) How are eddy currents reduced in a metallic core? (ii) Give two uses of eddy currents.

26. Current in a circuit falls from 5 A to 0 A in 0.1s. If an average emf of

200V induced, give an estimate of the self-inductance of the circuit.

27. Two identical loops, one of copper and the other of aluminium, are

rotated with the same angular speed in the same magnetic field.

Compare (i) the induced emf and (ii) the current produced in the two

coils. Justify your answer.

28. A coil Q is connected to low voltage bulb B and placed near another coil P is shown in the figure. Give reason to explain the following observations: (a) The bulb ‘B’ lights. (b) Bulb gets dimmer if the coil Q is moved towards left.


29. Mention the factors on which the resonant frequency of a series LCR

circuit depends. Plot a graph showing variation of impedance of a series

LCR circuit with the frequency of the applied a.c. source.

30. (a) Distinguish between the terms resistance, reactance and

impedance of an a.c. circuit.

(b) A 100µF capacitor in series with a 40Ω resistance is connected to a

100V, 60 Hz supply. Calculate (i) the reactance (ii) the impedance and

(iii) maximum current in the circuit.

31. A circular coil of radius 8cm and 20cm turns rotates about its vertical

diameter with an angular speed of 50 s-1 in a uniform horizontal

magnetic field of magnitude 3 x 10-2T. Find the maximum and average

value of emf induced in the coil.

32. State the underling principle of an a.c. generator. Write the relationship

between the peak value and rms value of alternating voltage.

33. In the following circuit, calculate (i) the capacitance of the capacitor if the power factor of the circuit is unity and (ii) the Q- factor of the

circuit.

34. An inductor 200 mH, a capacitor C and a resistor 10 ohm are connected

in series with a 100 V, 50 s-1 a.c. source. If the current and voltage are in

phase with each other, calculate the capacitance of the capacitor.

35. A capacitor and a resistor are connected in series with an a.c. source. If

the potential difference across C,R are 120V, 90 V respectively and if the

rms current of the circuit is 3 A, calculate the (i) impedance, (ii) power

factor of the circuit.

36. An alternating voltage of frequency f is applied across a series LCR

circuit. Let fr be the resonant frequency for the circuit. Will the current

lag, lead of remain in phase with the applied voltage when (i) f>fr (ii)

f<fr? Explain your answer in each case.

37. A conducting rod of length l is moved in a magnetic field of magnitude B

with velocity v such that the arrangement is mutually perpendicular.

Prove that the emf induced in the rod is ׀ɛ׀= Blv.

38. Derive an expression for the impedance of an a.c. circuit consisting of an

inductor, capacitor and a resistor.

39. Obtain the expression for the mutual inductance of a pair of coaxial

circular coils of radii r and R(R >r) placed with their centers coinciding.

40. A jet plane is travelling west at 450 ms - 1. If the horizontal component of

earth’s magnetic field at that place is 4 x10- 4 tesla and the angle of dip is

30°, find the emf induced between the ends of wings having a span of 30

m.

41. A town situated 20 km away from a power plant generating power at 440 V, requires 600kw of electric power at 220V. The resistance of the two wire lines carrying power is 0.4Ω per km. The town gets power from the line through a 3000-220V step down transformer at a substation in the town. (i) Find the line power losses in the form of heat. (ii) How much power must the plant supply, assuming there is negligible power loss due to leakage? (iii) Characteristics the step up transformer at the plant.

42. Define self-inductance of a coil. Show that magnetic energy required to

build up the current I in a coil of self-inductance L is given by ½LI2.

43. State Lenz’s law. A metal rod held horizontally along east-west direction, is allowed to fall under gravity. Will there be an emf induced at its ends? Justify your answer.

44. A Resistor of 200Ω and a capacitor of 15.0μF are connected in series to a 200 V, 50 Hz ac source.(i) Calculate the current in the circuit; (b) Calculate the rms voltage across the resistor and the capacitor. Is the algebraic sum of these voltages more than the source voltage? If yes, resolve the paradox. Long Answer Type o A

[5 marks each] o


45. (a) What is induced emf? Write Faraday’s law of electromagnetic induction. Express it mathematically. (b) A Conducting rod of length l with one end fixed, is rotated with a uniform angular speed ɷ in a vertical plane, normal to a uniform magnetic field B. deduce an expression for the emf induced in this rod. (c) In India domestic power supply is at 220V, 50Hz, while in USA it is 110V, 50Hz. Give one advantage and one disadvantage of 220V supply over 110V supply.

46. Three students X, Y, and Z performed an experiment for studying the variation of alternating currents with angular frequency in a series LCR circuit and obtained the graphs shown below. They all used a.c. sources of the same r.m.s. value and inductances of the same value. What can we (qualitatively) conclude about the (i) capacitance value (ii) resistance values used by them? In which case will the quality factor be maximum? What can we conclude about nature of the impedance of the set up at frequency ὠo?

47. (a) The given graphs represent the variation of the opposition offered by the circuit to flow of alternating current with frequency of the applied emf. Identify the circuit element corresponding to each graph.

(b) A Circuit is set up by connecting L=100 mH, C= 5µF and R=100Ω in series. An alternating emf of 150 2 Volt. 500/Hz is applied across this series combination. Calculate the impedance of circuit. What is the average power dissipated in (i) the resistor (ii) the capacitor (iii) the inductor and (iv) the complete circuit.

****************************************************************************************************


1. Identify the E.M. wave that is used in burglar alarms. Give its

wavelength and frequency.

2. When can a charge act as a source of electromagnetic waves?

3. Which part of electromagnetic spectrum has highest frequency?

4. What is the source of X-ray? 5. Identify the em waves used in remote control.

6. Which radiation is released in nuclear reactions? OR Name the radiation

involve in nuclear reaction.

7. Write the use of infrared waves .

8. Name the part of electromagnetic spectrum of wavelength 10-2m and mention its applications?

9. Which part of electromagnetic spectrum has largest penetrating power?

What is its frequency range?

10. Write the following radiations in an ascending order in respect of their

frequencies: X-rays, microwaves, ultraviolet rays and radio waves.

11. What is the ratio of speed of gamma rays and radio waves in air?

12. Name the electromagnetic radiations used for viewing objects through haze

and fog.

13. Name the electromagnetic radiations used for studying crystal structure of

solids.

14. What is the ratio of speed of gamma rays and radio waves in vacuum?

15. Which part of electromagnetic spectrum does the wavelength 10 -10 m

corresponds to?

16. What is the phase difference between electric and magnetic field vectors?

17. Give a reason to show that micro waves are batter carrier of signal for long

range transmission than radio waves.


18. A plane electromagnetic wave travels in vacuum along z-direction. What can you

say about the directions of its electric and magnetic field vectors? If the

frequency of the wave is 30 MHz, what is its wavelength?

19. Name the characteristics of electromagnetic waves that

(i) increases

(ii) remains constant

in the electromagnetic spectrum as one moves from radio wave region towards

ultraviolet region.

20. What modification was made by Maxwell in Ampere circuital law?

21. find the wave length of electromagnetic waves of frequency 5x1019 Hz in free

space. Give its two applications.

22. Write the electromagnetic wave whose wavelength is 1nm to 10-3 nm & write its

one application?

23. A radio can tune in to any station in the 7.5 MHz to 12 MHz band. What is the

corresponding wavelength band?

24. Name the part of the electromagnetic spectrum of frequency Hz1010 and mention

its application.

25. Identify the radiation and give their one application

(I)Is used for studying crystal structure.

(ii)Produces intense heating effect.

26. Write the following radiations in an ascending order with respect of their

frequencies Gamma rays, Infra red, Visible light, Radio waves.

27. Mentioned four important facts about em waves.

Short Answer type Questions [3mark each]

28. Which constituent radiation of electromagnetic spectrum is used in (1) radar (2) to photograph internal parts human body (3) for taking photograph of the sky during light and foggy condition? Give one reason for your answer in each case.

29. When can a charge act as source of electromagnetic wave? How are the

directions of electric and magnetic fields vectors, in an electromagnetic

wave, related to each other and to the direction of propagation of the wave?

Which physical quantity has the same value for the waves belonging to the

different parts of the electromagnetic spectrum?

30. The velocity of propagation (in vacuum) and the frequency of (i) X-rays

and (ii) Radio waves are denoted by (vx , nx) and (vr , nr) respectively. How

do the values of

(i) vx and vr

(ii) nx and nr

Compare with each other?

31. Why are infrared radiations referred to as heat waves also? Name the

radiations which are next to these radiations in electromagnetic spectrum

having

(i) Shorter wavelength.

(ii) Longer wavelength.

32. The oscillating magnetic field in a plane EM wave is given by

(i) By = xt 300102sin108 106 Tesla

(i) Calculate the amplitude of Electric field.

(ii) Write down the expression for the oscillating electric field.

33. Given below are some famous numbers associated with

electromagnetic radiations indifferent contexts in physics. State the part of the

electromagnetic spectrum to which each belongs.

(a) 21 cm (wavelength emitted by atomic hydrogen in interstellar space).

(b) 1057 MHz (frequency of radiation arising from two close energy levels in

hydrogen; known as Lamb shift).

(c) 2.7 K [temperature associated with the isotropic radiation filling all

space-thought to be a relic of the ‘big-bang’ origin of the universe].

(d) 5890 Å - 5896 Å [double lines of sodium]

(e) 14.4 keV [energy of a particular transition in 57Fe nucleus associated with a

famous high resolution spectroscopic method (Mössbauer spectroscopy)].

35. Identify the following part of em waves which (a) has its wavelength range between 390 nm & 770 nm (b) Is absorbed by ozone layer. . (c) Produces intense heating effect.

OPTICS


1. An object is held at the principal focus of a concave lens of focal length f. Where is the image formed?

2. Light waves can be polarized while sound waves cannot be, why?

3. Why do welders wear special dark glass goggles or face masks with glass window? Justify your answer.

4. Write the two differences between interference and diffraction.

5. In which direction relative to the normal, does a ray bend, when it enters obliquely a medium in which its speed is increased?

6. What is the focal length of a plane mirror?

7. What happen to the value of the focal length of a convex lens and concave mirror they immersed in water?

8. What is the geometrical shape of the wavefront when a plane wave

passes through a convex lens?

9. A diverging lens of focal length ‘F’ is cut into two identical parts each forming a plano-concave lens. What is the focal length of each part?

10. How the angular separation of interference fringes in Young’s double slit experiment change when the distance between the slits and screen is doubled?

Short Answer Type Questions-I [2 marks each]

11. A glass lens of refractive index 1.45 disappears when immersed in a

liquid. What is the value of refractive index of the liquid?

12. A converging lens is kept co-axially in contact with a diverging lens – both the lenses being of equal focal lengths. What is the focal length of the combination?

13. For the same value of angle incidence, the angles of refraction in three media A, B and C are 15°, 25° and 35° respectively. In which medium would the velocity of light be minimum?

14. In a single-slit diffraction experiment, the width of the slit is made double the original width. How does this affect the size and intensity of the central diffraction band?

15. How does the fringe width, in Young’s double-slit experiment, change when the distance of separation between the slits and screen is doubled?

16. (i) What is the relation between critical angle and refractive index of a material?

(ii) Does critical angle depend on the colour of light? Explain. 17. A convex lens has power 10D. It is immersed in a liquid, then it behaves as

concave lens having focal length 50 cm. Find refractive index of the liquid

(given 5.1ga )

18. Explain refraction of wave front using Huygens's Principle.

19. In Young’s double slit experiment if the distance between two slits is

halved and distance between the slits and the screen is doubled , then

what will be the effect on fringe width

20. How the intensity of maxima and minima in the Young will’s double

slit experiment change, if one of the two slits is covered by a transparent

paper which transmits only half of the light intensity?

21. Draw a labeled ray diagram showing the formation of image by a compound microscope. State the expression for its magnifying power.

22. How does the fringe width of interference fringes change, when the

whole apparatus of Young’s double slit experiment is immersed in a

liquid if refractive index 1.3?

23. State reasons to explain these observations-

a. The bluish colour predominates in clear sky.

b. Violet color is seen at the bottom of the spectrum when white light is

dispersed by a prism.

24. A convex lens made of glass of refractive index µl, is immersed in

medium of refractive index µm. How will the lens behave when µl>µm.

25. A ray is to be deviated through 90° by a right- angled isosceles prism. What should be the minimum refractive index of the material of the prism?

26. Two thin lenses of power +7D and -3D are in contact.What is the focal length of the combination?

27. Explain how the focal length of a convex lens changes with increase in wavelength of incident light.

28. On what factors does (i) magnifying power and (ii) resolving power of a

compound microscope depend? 29. Define refractive index of a transparent medium. A ray of light passes through a triangular prism. Plot a graph showing the variation of the angle of deviation with the angle of incidence. 30. Define the term ‘linearly polarized light.’ When does the intensity of transmitted light become maximum, when a polaroid sheet is rotated between two crossed polaroids? Short Answer Type Questions-II [3 marks each]

31. Draw a labelled ray diagram of a reflecting telescope. Mention its two

advantages over the refracting telescope.

32. You are given three lenses having powers P and Apertures A as follow : P1 = 6D, A1 = 3cm P2 = 3D, A2 = 15cm P3 = 12D, A3 = 1.5cm

33. What is an unpolarized light and polarized light? Under what condition

does a beam of light reflected by a transparent medium become plane

polarized? Use this condition to establish a relation between the angle

of incidence and the refractive index of the transparent medium.

34. In a single slit diffraction experiment, the width of the slit is made double the original width. How does this affect the size and intensity of the central diffraction band? Draw a plot of the intensity distribution.

35. State Mauls law and draw a graph showing the variation of intensity of

polarized light transmitted by an analyzer. A polarizer and an analyzer

are so oriented that intensity of transmitted light is maximum. If the

analyzer is rotated through 600, what fraction of the maximum light is

transmitted?

36. (i)Derive the mirror formula which gives the relation between f, v

and u.

(ii)A convex lens of refractive index n1 is held in a medium of

refractive index n2. Trace the path of refracted rays of a parallel beam

of light incident on the lens when (i) n2>n1 and (ii) ) n2=n1

37. A convex lens of focal length f1 is kept in contact with a concave

lens of focal length f2. Find the focal length of the combination.

38. A parallel beam of light of 600nm falls on a narrow slit and the resulting

diffraction pattern is observed on a screen 1.2 m away. It is observed

that the first minimum is at a distance of 3mm away from the centre of

the screen. Calculate the width of the slit.

39. A parallel beam of light of 500nm falls on a narrow slit and the resulting

diffraction pattern is observed on a screen 1m away. It is observed that

the first minimum is at a distance of 2.5mm away from the centre of the

screen. Calculate the width of the slit.

40. Draw a labelled ray diagram of a reflecting type telescope. Write its any two advantage over refracting type telescope.

41. State Huygens’s principle. Show, with the help of a suitable diagram,

how this principle is used to obtain the diffraction pattern by a single

slit.

a. What is meant by ‘normal adjustment’ of an astronomical telescope?

Trace the path of rays from a distant object through a refracting

astronomical telescope in normal adjustment. Derive an expression

for its magnifying power and length of tube in this position.

42. How would the length of the day be affected if there were no atmosphere around the earth? Explain your answer with the help of a diagram.

43. With the help of Huygens principle explain laws of refraction. And draw

refracted wavefront when a plane wavefront incident on a concave

mirror.

44. A parallel beam of light of 500 nm falls on a narrow slit and the resulting diffraction pattern is observed on a screen 1 m away. It is observed that the first minimum is at a distance of 2.5 mm from the centre of the screen. Calculate the width of the slit.

45. Draw the ray diagram of compound microscope in normal adjustment

and hence find the magnifying power of it in normal adjustment. How

does its magnifying power and resolving power change on (i) increasing

the focal lengths of the two lenses (ii) using the light of higher

wavelength

46. Find a relation for resolving power of a microscope. How is the

resolving power of a microscope affected when,

(i) The wavelength of illuminating radiations is decreased?

(ii) The diameter of the objective lens is decreased?

Justify your answer.

47. A right angled crown glass prism with critical angle 410 is placed before an

object PQ, in two positions as shown in the figure(i) and (ii).Trace the paths

of the rays from P and Q passing through the prisms in the two cases.

48. A compound microscope with a objective of 1.0 cm focal length and an eye-

piece of 2.0 cm focal length has a tube of length of 20 cm. Calculate the

magnifying power of the microscope, if the final image is formed at the near

point of the eye.


49. Draw the graph showing the variation of angle of deviation with angle

of incidence for a monochromatic ray of light passing through a prism of

angle A. Deduce an expression for its refractive index in terms angle of

minimum deviation and angle of prism?

a. A right angled isosceles glass prism is made from glass of refractive

index 1.5. Show that a ray of light incident normally on:

(i)One of the equal sides of this prism is deviated through 900

ii) The hypotenuse of this prism is deviated through 1800.

50. What are coherent sources of light? State two conditions for two light sources

to be coherent. Derive a mathematical expression for fringe width if

interference fringe obtained in Young’s Double Slit Experiment with the help

of a suitable diagram.

51. Explain total internal reflection. A light beam is incident on the

boundary between two transparent media. At a particular angle of

incidence the reflected ray is perpendicular to the refracted ray. Obtain

the expression this angle of incidence. Does this expression depend on

the wavelength of light used?

52. State Huygens principle for reflection of plane wave front at a plane

reflection surface. Construct the corresponding reflected wave front.

Using this diagram prove the laws of reflection.

53. A spherical surface, of radius of curvature R, and of refractive index µ2, is placed in a medium of refractive index µ1 where µ1 < µ2. The surface produces a real image of an object kept in front of it. Using appropriate assumptions and sign conventions, derive a relationship between the object distance, image distance, R, µ1 and µ2. Under what conditions this surface diverges a ray incident on it? For the same angle of incidence the angle of refraction in three different media A, B and C are

15º, 25º and 35º respectively. In which medium the velocity of light is minimum?

54. Two lenses of power 10 D and -5D are placed in contact.

a. Calculate the power of lens combination.

b. Where should an object is held from the lenses, so as to obtain a

virtual image of magnification 2.

55. (i) What is interference of light? Write two essential conditions for

sustained interference pattern to be produced on the screen. What is the

effect on interference pattern in Young’s double slit experiment, when

1. screen is moved closer to the plane of slits, 2. Separation between two slits is increased?

(ii).Draw a graph showing the variation of intensity versus the position on

the screen in Young’s double slit experiment, when

(a) Both the slits are opened and

(b) One of the slits is closed.

56. A convex lens made up of glass of refractive index 1.5 is dipped, in turn, in: (i) medium A of refractive index 1.65 (ii) medium B of refractive index 1.33 Explain, giving reasons, whether it will behave as a converging lens or a diverging lens in each of these two media.

57. Which of the following waves can be polarised (i) x-rays (ii) sound

waves? Give reasons. Two polaroids are used to study polarisation. One of them (the polariser) is kept fixed and the other (the analyser) is initially kept with its axis parallel to the polariser. The analyser is then rotated through angles of 45o, 90o and 180o in turn. How would the intensity of light coming out of analyser be affected for these angles of rotation, as compared to the initial intensity and why?

58. What is diffraction of light? Derive an expression for the width of the central maxima due diffraction of light at a single slit. Draw a graph showing the variation of intensity with phase difference or path difference in a single slit experiment.

59. What happens to the width of the central maxima if the whole apparatus is immersed in water and why? How would the diffraction pattern of a single slit be affected when: (i) the width of the slit is decreased? (ii) the monochromatic source of light is replaced by a source of white light? How is the width of central maxima affected (iii) on increasing the

wavelength of light used (iv) ) on increasing width of the slit?

60. Derive a relation between the focal length of a lens and its radii of curvature.

61. Draw a ray diagram to show the formation of image of an object placed between the pole and and focus of a concave mirror. Write two characteristics of the image formed. Using the diagram, derive the relation between object distance u, image distance v and focal length f of the concave mirror. Draw the graph showing the variation of v with u.

62. What is plane polarised light? Two polaroids are placed at 90° to each other and the transmitted intensity is zero. What happens when one more polaroid is placed between these two, bisecting the angle between them ? How will the intensity of transmitted light vary on further rotating the third polaroid?

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Atoms & Nuclei

Very Short Type Questions (1 mark each)

1. What is the SI unit of activity of a radioactive sample.. Define the unit

2. A radioactive nucleus ‘A’ decays as given below:

β γ A A1 A2

If the mass number & atomic number of A1 are 180 & 73 respectively, find

the mass number & atomic number of A & A2

3. What is the value of impact parameter for head on collision?

4. Write two important inferences drawn from Rutherford’s alpha particles scattering experiment.

5. Name the series of hydrogen spectrum which least wave length

6. Why should an unstable nucleus emit an α particle and not an individual

proton and neutron?

7. Write the nuclear reaction for β decay of 32P15.

8. Define decay constant of a radioactive element. 9. Can it be concluded from beta decay that electrons exist inside the

nucleus? 10. What is the ratio of radii of two nuclei of mass numbers A1 and A2? 11. Which one has highest binding energy per nucleon

235U92 &

16O8.

12. Write the relation between half life and decay constant of a radioactive sample.

13. What is the ratio of the radii of two nuclei of mass number 27 & 8 ? 14. Heavy water is often used as a moderator in thermal nuclear

reactors.’ Give reason.

15. Mention any one difference between atomic reactions and nuclear

reactions

Short Answer Type Questions-I [2marks each]

16. A radioactive nucleus undergoes a series of decay as follows

A α A1 β A2 α A3 γ A4

The mass no and atomic no of A are 180 and 72 respectively, what

are this numbers for A4?

17. Explain, with the help of a nuclear reaction in each of the following

cases, how the neutron to proton ratio changes during (i) alpha-decay

(ii) beta-decay?

18. Write any four characteristics of nuclear forces. 19. Name the series of hydrogen spectrum lying in ultraviolet and visible

region? 20. Why is nuclear fusion not possible in laboratory? 21. Write two characteristic feature of nuclear force which distinguish it

from coulomb’s force. 22. What is the longest wavelength photon that can ionize a hydrogen

atom in its ground state? Specify the type of radiation. 23. Define Mass-defect. Give the formula to find out the mass defect. 24. Plot the graph showing the variation of Potential energy of a pair of

nucleons as a function of their separation. What important conclusions can be drawn from this graph?

25. Give the differences between β-& β+ decay reactions. 26. Give the Postulates of Bohr’s Model of atom. What is the physical

significance of negative sign in the expression En =−13.6 /𝑛2 eV. 27. Calculate the ratio of energies of photons produced due to transition

of electron of hydrogen atom from its,(i) Second permitted energy level to the first level, and (ii) Highest permitted energy level to the second permitted level

Short Answer Type Questions-II [3 marks each] 28. Write the laws of radioactive decay. Find expression

N=N0e- λt

29. A neutron is absorbed by 3Li6 nucleus with the subsequent emission of

alpha particle (a)write the corresponding nuclear reaction (b)calculate

the energy released in the reaction Given

m(Li)=6.015126 amu mn=1.008665amu m(α) =4.0026044amu

m(tritium)=3.010000 amu

30. The ground state energy of hydrogen atom is -13.6 eV. If an electron

transits from an energy level -0.85 eV,

(i)Calculate the wavelength of the spectral line emitted.

(ii)to which series of spectral lines this wavelength belong

31. Calculate the binding energy per nucleon of 20Ca40 nucleus Given

m (20Ca40)=39.962589 amu m n=1.008665amu mp =1.007825amu

32. State Bohr’s postulate for the ‘permitted orbits’ for the electron in a

hydrogen atom. Use this postulate to prove that the circumference of

the nth permitted orbit for the electron can contain exactly n

wavelengths of the de-Broglie wavelength associated with the electron

in that orbit.

33. The total energy of an electron in the first excited state of the hydrogen atom is about –3.4eV. (a) What is the kinetic energy of the electron in this state? (b) What is the potential energy of the electron in this state? (c) Which of the answers above would change if the choice of the zero of

potential energy is changed?

34. The half-life of a radioactive substance is 30 sec. Calculate :

(i) The decay constant, and

(ii) Time taken for the sample to decay to 3/4 th of its initial value.

35. The half-life of U 238 undergoing α-decay is 4.5 × 109 years. What is the activity of 1g sample of 238 U92?

36. Draw the graph showing the variation of binding energy per nucleon with mass number for different nuclei. explain it.. State with reason why light nuclei usually undergo nuclear fusion?

37. Define disintegration constant and mean life of a radioactive substance

and how they are related to each other.

38. Draw a neat schematic diagram showing arrangement of the Geiger- Marsden experiment. Also give the plot showing the variation of Number of scattered particles detected with scattering angle.

39. Discuss about the different spectral lines emitted by Hydrogen atom.

Long Answer Type Questions [5 marks each] 40. (a) Define decay rate or activity of a substance.

(b)Show that the activity ‘R’ of a sample of a radionuclide is related to the number of radioactive nuclei ’N’ at same instant by the expression R = λN, (c) Define two units of activity. How are they related?

Dual nature of Matter & Radiation


1. Give the plot showing the variation of Photoelectric current with intensity of light.

2. Give any two properties of photon.

3. With that purpose was famous Davisson-Germer experiment with

electrons performed?

4. Show graphically how the stopping potential for a given photosensitive

surface varies with the frequency of incident light.

5. What is the effect on the velocity of the emitted photoelectrons if the

wavelength of the incident light is decreased?

6. Two metals A and B have work function 4 eV and 10 eV respectively, which

metal has the higher threshold wavelength?

7. What are the applications of photoelectric cell.

8. The maximum kinetic energy of a photoelectron is 3 eV. What is its stopping potential?

9. Why is it difficult to remove a free electron from copper than sodium?

10. The wavelength of electromagnetic radiation is doubled. What will happen to the energy of photon?

11. Two beams, one of red light and other of blue light, of same intensity

are incident on a metallic surface to emit photoelectrons. Which one of the

two beams emits electrons of greater kinetic energy?

12. What is the rest mass of a photon?

13. How will the photoelectric current change on decreasing the wavelength of incident radiation for a given photosensitive material?


14. An electron is accelerated through a potential difference of 144 volts.

What is the de-Broglie wavelength associated with it? To which part of the

electromagnetic spectrum does this wavelength correspond?

15. Are matter waves electromagnetic? What is the momentum of a

photon of Frequency ?

16. The given graphs show the variation of photo electric current (I) with the applied voltage (V) for two different materials and for two different intensities of the incident radiations. Identify the pairs of curves that

correspond to different materials but same intensity of incident radiations.

17. Draw the graph showing the variation of photo current with anode

potential for

(a) Same frequency but different intensities I3 > I2 > I1 of the

incident radiation

(b) Same intensity but different frequencies ν3 > ν 2 > ν 1 of the

incident radiation.

18. The two lines A and B shows in the graph plot the de-Broglie

wavelength λ as a function of 1/√V for two particles having the same charge. Which of the two represents the particle of heavier mass?

18. The frequency of the incident light is doubled. What will be the K.E of

the electrons emitted? 19. What is photoelectric effect? Do all the metals are photo sensitive to

ultraviolet? Name the law on which the phenomenon depends upon. 20. Derive the relation for finding the de-Broglie wavelength of an electron.

21. Why are alkali metals most suited for photoelectric emission? 22. Name the experiment for which the following graph, showing the

variation of intensity of scattered electrons with the angle of scattering, was obtained.

Also name the important hypothesis that was confirmed by this experiment

23. Light from a bulb is falling on a wooden table but no photoelectrons are emitted. Why?

24. A proton and an electron have same kinetic energy. Which one has

smaller de Broglie wavelength and why?

25. The work function of copper is 4.0 eV. If two photons, each of energy 2.1 eV strike with some electrons of copper, will the emission be possible?

26. A graph shows the variation of stopping potential v/s Frequency of the incident radiation for two photosensitive metals X and Y. Which of the metals has larger threshold wavelength and what will be their ratio?

27. An electron and a proton are moving in the same direction and possess some Kinetic energy. Find the ratio of De-Broglie wavelengths associated with these particles Short Answer Type Questions-II [3 marks each]

28. Define the terms threshold frequency and stopping potential in relation to the phenomenon of photoelectric effect. How is the photoelectric current affected on increasing the (i) frequency (ii) intensity of the incident radiations and why?

29. Plot a graph showing the variation of stopping potential with the

frequency of incident radiation for two different photosensitive materials

having work functions 1W and )( 212 WWW .

On what factors does the (i) slope and (ii) intercept of the lines depend?

30. Use Einstein’s photo electric equation to show that there must exist a

threshold frequency for each photo sensitive surface. Radiations of

frequencies ν1 and ν2 are made to fall, in turn, on a photo sensitive surface.

The stopping potentials required for stopping the most energetic emitted

photoelectrons in the two cases are V1 and V2 respectively. Obtain a

formula for calculating Planck’s constant and the threshold frequency in

terms of these parameters.

31. X-rays of wavelength 0.82Å fall on a metallic surface. Calculate the de-

Broglie wavelength of the emitted photoelectrons. Neglect the work

function of the surface

32. The following table gives the values of work function for a few photo

sensitive metals

S.No. Metal Work Function (eV)

1. Na 1.92

2. K 2.15

3. Mo 4.17

If each of these metals is exposed to radiations of wavelength 300 nm,

which of them will not emit photo electrons and why?

33. By how much would the stopping potential for a given photosensitive

surface go up if the frequency of the incident radiations were to be

increased from 4 x 1015 Hz to 8 x 1015 Hz? Given h = 6.4 x 10-34 J-s, e =

1.6 x 10-19 C and c = 3 x 108 ms-1

34. The work function of a metal is 2.50eV. When light of frequency 7*1014

Hz is incident on the metal surface, photoemission of electrons occurs. Find

the (a) maximum kinetic energy of the emitted photoelectrons. (b)

Stopping potential and (c) maximum speed of the emitted photoelectrons?

35. Define the following terms. a. Stopping Potential b. Threshold frequency c. Work function.

36. What is the de-Broglie wavelength associated with (a) an electron moving with a speed of 5.4 X 106 m/s, and (b) a ball of mass 150g travelling at 30.0m/s?

37. The work function of potassium is 2.0 eV. What is the threshold wavelength for potassium? If light of 2000 Å falls on its surface, calculate the maximum kinetic energy of the ejected photoelectrons.

38. Describe Davisson and Germer experiment to establish the wave nature of electrons. Draw a labeled diagram of the apparatus used.

39. What is Einstein’s photoelectric equation? What does the slope of this equation’s graph represent?

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Question bank

CLASS XII PHYSICS

Electronic Devices


1. How does resistivity of a semiconductor change with rise in its

temperature?

2. What is the order of energy gap in a semiconductor?

3. Give the ratio of the number of holes and the number of conduction electrons in an intrinsic semiconductor.

4. State the reason, why a photodiode is usually operated at reverse bias?

5. How does the width of the depletion layer of a p-n junction diode change with decrease in reverse bias?

6. The resistance of p-n junction diode decreases when forward biased. Why? 7. A square wave form is applied to the p-n junction diode as shown. Draw

the output wave form:-

8. At what temperature would an intrinsic semiconductor behave like a perfect insulator?

9. Why is the base of transistor made thin and lightly doped? 10. How does the collector current change in a junction transistor, if the base

region has larger width? 11. Give any two advantages of LEDs over conventional incandescent low

power lamps. 12. Plot V-I characteristic curve of a Solar cell. 13. Give any two uses of LEDs. 14. Does a solar cell always requires sunlight for its working? 15. Draw the diagram showing the wave form of Frequency Modulated Wave.

RV1

V1

16. A transistor is being used as a common emitter amplifier. What is the

value of phase difference, if any, between the collector-emitter voltage and input signal?


17. Explain how emf is generated by a Solar cell when light falls on it.

18. What are the important criteria for the selection of a material for solar cell fabrication?

19. Define the transconductance of a transistor. On what factors does it depend?

20. What is an intrinsic semiconductor? How can you convert an intrinsic semiconductor into N-type extrinsic semiconductor?

21. What is a cell in Mobile Telephony? How it helps in communication systems.

22. In a Zener regulated power supply a Zener diode with Vz = 6.0V is used for regulation. The load current is to be 4.0mA and the unregulated input is 10.0V. What should be the value of series resistor Rs?

23. The current gain for common emitter amplifier is 59. If the emitter current is 6 mA, find (i) base current and (ii) collector current.

24. Draw a circuit diagram of a common emitter amplifier using n-p-n transistor. What is the phase difference between the input signal and output signal?

25. In the following circuit, the two diodes, each with a forward resistance of 50Ω and with infinite backward resistance are connected across the battery of voltage 6V. Find the current through 100Ω resistance:-

26. Draw the truth table for the gate shown here:

1D

2D

150

50

100V6

A

B

1y

2y

y

27. Visible light photons are known to have energies ranging from (nearly) 1.8 eV to 2.8 eV. Use this information to reason out why silicon is not a suitable semiconductor for designing LED’s?

28. Give the logic symbol for an AND gate. Draw the

output wave form for AND gate input wave forms A and B.

29. For the digital circuit given below, write the truth table showing the outputs Y1, Y2 and Y3 for all possible inputs at A and B

30. The input resistance of a CE amplifier is 2 K and a current gain is 20. If the load resistance is 5 KW. Calculate:

(i) The voltage gain of the amplifier and (ii) The trans-conductance of transistor used.

31. In only one of the circuits given below the lamp L lights. Which circuit is it?

Give reason for your answer.


32. (a) Explain the formation of depletion layer and potential barrier in

a p-n junction.

(b) In the figure given below, the input waveform is converted into the

output waveform by a device ‘X’. Name the device and draw its circuit

diagram.

A

B

33. Two semiconductor materials X and Y shown in the figure are made by doping germanium crystal with indium and arsenic respectively. The two are joined end to end and connected to a battery as shown. (i) Will the junction be forward or reverse biased? (ii) Sketch a V – I graph for this arrangement.

34. Give the logic symbol of AND gate. Explain with the help of a circuit diagram, how this gate is realized in practice.

35. Give the logic symbol of OR gate. Explain with the help of a circuit diagram, how this gate is realized in practice.

36. The input resistance of a silicon transistor is 66Ω. Its base current is changed by 15 μA which results in the change in collector current by 2 mA. This transistor is used as a common emitter amplifier with a load resistance of 5 k. Calculate:

(i) Current gain αa.c. (ii) Trans-conductance ‘gm’, and (ii) Voltage gains ‘A’ of the amplifier.

37. For a CE transistor amplifier, the audio signal voltage across the collector resistance of 2.0 kΩ is 2.0V. Suppose the current amplification factor of the transistor is 100, what should be the value of RB in series with VBB supply of 2.0 V if the dc base current has to be 10 times the signal current? Also calculate the dc drop across the collector resistance.

38. Write the truth table for circuit given in fig consisting of NOR gates only. Identify the logic operations ( OR, AND, NOT) performed by the two circuits.

X Y

39. Two signals A and B shown in the given figure are used as two-inputs of (i) AND gate (ii) NOR gate and (iii) NAND gate. Obtain the output each of the

three cases.

40. With the help of a labeled circuit diagram explain how an n-p-n

transistor can be used as an amplifier in common emitter configuration. Explain how the input and output voltages are out to phase by 180o for a common emitter transistor amplifier.

41. In the circuit diagram given, a voltmeter V is connected across a lamp L. What changes would occur at lamp L and voltmeter V, if the resistor R is

reduced in value? Give reason for your answer.

****************************************************************************************************

Communication systems


1.Name the device fitted in the satellite which receives signals from Earth station and transmits them in different directions.

2.What is the cut-off frequency beyond which the ionosphere does not reflect electromagnetic radiations?

3.Optical and radio telescopes are built on the ground but X-ray astronomy is possible only from satellites orbiting the Earth. Why?

4.Name the type of communication in which the signal is a discrete and

binary coded version of the message of information.

5.How does the effective power radiated by an antenna vary with

wavelength?

6.Why TV signals are not transmitted using sky waves?

7.Explain the function of a repeater in a communication system.

8.What type of modulation is required for commercial broadcast of voice

signals?

9.Name the basic modes of communication systems.

10.What is meant by band-width?


11.Define the following terms (a) Attenuation (b) Amplification

12. What are different modes of propagation of radio waves?

13. Define modulation index. Why it should always be less than one?

14. State the condition under which a microwave oven heats up a food item

containing water molecules most efficiently.

15. Explain the function of a repeater in a communication system.

16. What should be the length of the dipole antenna for a carrier wave

frequency 3x108 Hz?

17. What is a cell in Mobile Telephony? How it helps in communication

systems.

18. What is a communication system? Mention the major constituents of a communication system.


19. Distinguish between ‘point to point’ and ‘broadcast’ communication modes.

Give one example of each.

20. The height of T.V tower at a place is 400mt. calculate the maximum range up

to which signal can be received and area of coverage? R = 6400km.

21. What does the term LOS communication mean? Name the types of waves that

are used for this communication. Which of the two-height of transmitting

antenna and height of receiving antenna - can affect the range over which this

mode of communication remains effective?

22. Explain the following terms:

(i) Ground wave propagation (ii) Space wave propagation (iii) Sky wave

propagation.

23. Derive an expression for the range into which signals transmitted by a T.V.

tower can receive.

24. For an amplitude modulated wave, the maximum amplitude is found to be

10V while the minimum amplitude is found to be 2V. Determine the modulation

index; μ. What would be the value of μ if the minimum amplitude is zero volt?

25. Block diagram of a receiver is shown in the figure:

(a) Identity ‘X’ and ‘Y’.

(b) Write their functions.

26. (a) Draw a block diagram of a simple modulator for obtaining AM signal.

(b) Why do we need carrier waves of very high frequency in the modulation of

signals? A carrier wave of peak voltage 20 V is used to transmit a message signal.

What should be the peak voltage of the modulating signal, in order to have a

modulation index of 80%?


27. (a) Draw the block diagram of a communication system.

(b) What is meant by ‘detection’ of a modulated carrier wave? Describe briefly

the essential steps for detection.

28. Define amplitude modulation. Derive an expression for an amplitude modulated wave. Hence state the sideband frequencies present in AM wave. *********************************************************************************

Prepared by : (i) SH RAVI ARORA PGT(PHY)

KV AFS UTARLAI

(ii) SH PAWAN KUMAR BALAI PGT(PHY)

KV AFS UTARLAI

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