SECTION-C 2 x 8 = 16
Note:-
i) Answer any two questions
ii) Every question carries eight marks.
iii) All are long answer type questions.
19. What is Doppler effect? Obtain an expression for the
apparent frequency ofsound heard when the source is in motion with
respect to an observer at rest?
20.Obtain an expression for the torque on a current carrying
loop placed in a uniform magnetic field. Describe the construction
and working of a moving coil galvanometer?
21.Explain the principle and working of a nuclear reactor with
the help of a labeled diagram.
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SENIOR INTER PHYSICS E/M
SECTION A
Note:
i. Answer all questions
ii. Each question carries two marks.
iii. All are very short answer type questions 10 x 2 = 20
1. What is Malus Law?
2. What is meant by the statement charge is quantized?
3. State Amperss law and Biot-Savart law
4. What happens to compass needles at the Earths poles?
5. Define magnetic flux?
6. What is the ratio of speed of infrared rays and ultraviolet
rays in vaccum.?
7. What is Photo electric effect
8. What do you understand by the phrase ground state atom?
9. Draw the circuit symbols for p-n-p and n-p-n transistors.
10. Define modulations. Why is it necessary?
SECTION B 6 X 4 = 24
Note:
i. Answer any six questions
ii. Each question carries four marks.
iii. All are short answer type questions
11. Define critical angle. Explain total internal reflection
using a neat diagram?
12. How do you determine the resolving power of your eye?
13. Derive an equation for the couple acting on a electric
dipole in a uniform electric field.?
14. Derive an expression for the capacitance of a parallel plate
capacitor.
15. State Kirchhoffs laws for electrical network. Using these
laws deduce the condition for balancing in a wheat stone
bridge.
16. State the principle on which a transformer works. Describe
the working of a transformer with necessary theory.
17. What are the limitations of Bohrs theory of hydrogen
atom
18. What is rectification? Explain the working of a full wave
rectifier?
SECTION-C 2 x 8 = 16
Note:-
i) Answer any two questions
ii) Every question carries eight marks.
iii) All are long answer type questions.
19. What is Doppler effect? Obtain an expression for the
apparent frequency of sound heard when the source is in motion with
respect to an observer at rest?
20.Obtain an expression for the torque on a current carrying
loop placed in a uniform magnetic field. Describe the construction
and working of a moving coil galvanometer?
21.Explain the principle and working of a nuclear reactor with
the help of a labeled diagram.
ANSWERS
SECTION-A
1. The intensity of the polarized light transmitted through the
analyzer is proportional to square of cosine of the angle between
the plane of transmission of analyzer and the plane of transmission
of polarizer".?
I=I0 cos2
Where
I0 = intensity of the polarized light after passing through the
polarizer.
= angle between the planes of transmission of the analyzer and
the polariser.
2. The change on anybody can be expressed as in integral
multiple of changes of electron i.e q= ne, where 'n' is a integer
,e= 1.6 x 10-19 C. Therefore charge is said to be quantized.
3. Ampere's Law:- The line integral of the intensity of magnetic
induction around a closed path is equal to '0' times the total
current enclosed in it.
Implies B . dl = o i
Biot-savart's Law:- Biot-savart's law states that the intensity
of magnetic induction (dB) due to a small element is directly
proportional to the current(i), length of element (dl), since of
the angle between radius vectors (r) and 'dl' and inversely
proportional to the square of distance of the point from current
element.
Implies dB = .
4. Compass needles doesn't work at magnetic poles of the earth
because, at poles BH=0.dip needle is vertical.
5. The magnetic flux over a given surface is defined as the
product of the area of the surface and the component of the
magnetic field normal to the surface 'B cosQ'.
= B . A = (B. n) A
Where n= unit vector along the normal drawn to the plane of the
surface.
6. Electromagnetic waves of different wave lengths have the same
velocity in vacuum. The ratio of infrared and ultraviolet rays is
1:1
7. When a light of sufficient energy is made to incident on a
photo metal, electrons are emitted. This phenomena is known as
photo electric effect.
8. An unexcited atom is called ground state atom.
9.
CollectorCollector
EmitterEmitter
BaseBasen-p-n Transmitorp-n-p Transmitor
10. Modulation:- the process of combining low frequency audio
signals with high frequency electromagnetic signals is called
modulation.
Necessity of modulation :-
i. Low frequencies cannot be transmitted to long distances.
ii. To limit the size of antenna.
SECTION-B
11. When light travels from denser medium to rares medium, the
angle of incidence, for which angle of refraction is 90oC is called
Critical Angle.
Explanation:
When light ray travelling from denser medium towards rarer
medium is incident on the interface of two media at an angle
greater than critical angle, then it is totally reflected back into
denser medium. This phenomenon is called total internal
reflection.
B
Water-air interfaceRarer medium (Air)
O1 O2 O3 D O4
Denser medium (Water)
i N i1 N ic N i > ic N
Totally reflected rays C partially reflected rays
A
Explanation:
When light ray enters from denser medium to a rarer medium, it
bends away from normal as shown by the ray Ao, B.
The incident ray Ao, is partially reflected (O,C) and partially
refracted (O,B). Here angle of refraction r is greater than angle
of incidence increases, the angle of refraction also increases and
finally becomes as shown for ray Ao3. Here refracted ray Ao3D
grazes the interface. Now, if the angle of incidence is further
increased as shown for ray Ao3, the refraction is not possible and
the incident ray is totally reflected back into denser medium which
is called total internal reflection.
12. You can estimate the resolving power of your eye with a
simple experiment. Make black stripes of equal width separated by
white stripes. All the black stripes should be of equal width,
while the width of the intermediate white stripes should increase
as you go from the left to the right.
For example let all black stripes have a width of 5mm, let the
width of the first two white stripes be 0.5mm each, the next two
white stripes be 1 mm each, the next two 1.5mm each, etc paste this
pattern on a wall in a room (or) laboratory, at the height of your
eye.
Now watch the pattern, preferably with one eye. By moving away
or closer to the wall, find the position where you can just see
some two black stripes as separate stripes. All the black stripes
to the left of this stripe would merge into one another and would
not be distinguishable on the other hand, the black stripes which
separates the two regions, and measure the distance D of the wall
from you eye. Then is the resolution of your eye.
13. Consider an electric dipole having dipole moment P, and
length 2a placed in a uniform electric field E with an angle as
shown in figure.
a. The force acting an each charge is Eq
b. These two equal and unlike parallel forces form a couple.
c. It will try to rotate the dipole parallel to the electric
field. This is called moment of the couple.
E +Eq
2a
+q
-Eq
Moment of the couple = F x war distance between the two
forces
= F x AN
from le ABN, we have sin = => AN = ABsin
AN = 2asin (Since AB = 2a)
= Eq x 2asin = PE sin (Since P = q x 2a)
In vector form = P + E
14. A parallel plate capacitor consists of two large parallel
conducting plates separated by a small distance d
Surface charge density I +Q Area A
+ + + + + + + + + + + + + + +
d
E
- - - - - - - - - - - - - - - - - - -
Surface charge density -
II -Q
Let A be the Area of each plate andd be the distance between the
plates.
The two plates have +Q and -Q
Plate I has surface charge density + =
Plate II has surface charge density =
In the inner region between the plates I and II the electric
field due to the two charged plates add up
E = + = =
The direction of E is from positive plate to negative plate.
For uniform Electric field, potential difference is
V = Ed = .
The capacitance Cof the parallel plates capacitor
C = =
It depends on geometry and medium between plates.
15. a.Kirchoffs current law (or) First law:
The algebraic sum of all the current meeting at any junction is
zero.
i1 i5
i4
i2
i3
From kirchoffs current law
i1+i2 + i3 = i4 + i5
i1 + i2 + i3- i4 i5 = 0
This is based on law of conservation of charge
b. Kirchhoff's voltage law:
In any closed circuit the algebraic sum of the potential
differences is equal to zero. This law is based on law of
conservation of energies.
V = 0
+E
V3V2V1 R1 R2 R3
Sign convention:
1. when we move across resistor in the direction of current, the
potential drop across the resistor is taken as iR
2. when we move across the resistor in the opposite direction of
current, the potential drop across the resistor is taken as +
iR
3. if we move from negative terminal to positive terminal of a
cell then its emf is taken as positive.
4. If we move from positive terminal to negative terminal of a
cell, then its emf is taken as negative.
From the above figureE-IR1 IR2 IR3 = 0
E= IR1 + IR2 + IR3
I =
Wheat stones Bridge:
Wheat stone bridge consists of four resistances P, Q, R and S
connected as shown in figure to four junctions A, B, C and D.
between the junction A and C a battery of emf is connected. Between
the junctions B and D a Galvanometer G is connected.
B
P i3
G i1 Q
i2
R i4 s
Applying Kirchoffs first law at the junction B
i1 i3 ig = 0 (1)
for the junctionD
i2 +ig i4 = 0 (2)
applying Kirchoffs second law for the closed mesh ABDA, going in
the clockwise direction.
-i1P igG + i2R = 0 (3)
And for BCDB again going in the clockwise direction
-i3Q + i4S + igG = 0 (4)
When no current passing through the galvanometer, ig = 0.
The bridge is said to be balanced.
Using ig = 0 in above equations
i1 = i3 (5), i2 = i4 (6)
i1P = i2 R (6), i3Q = i4S (8)
Dividing equation (7) and (8)
= =
This is principle of wheat stone bridge.
16. A transformer is a device which transforms electric power.
In one circuit into electric power of same frequency in another
circuit. This works on the principle of mutual induction between
two circuits linked by a common magnetic flux. This transformation
of voltage is possible only with alternating current (AC) but not
with direct current (DC).
Construction: It consists of two coils P and S wound on a soft
iron core. The coil P is called Secondary coil. The AC input is
applied across the primary coil. The output is obtained across
secondary coil. To minimize eddy current losses, the core is
laminated.
Primary winding Secondary winding
P S
Working: when the alternating emf is applied to the primary coil
the current through the primary coil varies therefore, the magnetic
flux linked with the primary coil changes. Since the magnetic flux
is coupled to the secondary coil, the magnetic flux linked with
secondary also changes. As a result, an alternating emf of the same
frequency is induced across the secondary. The magnetic of induced
emf depends on the emf across primary and number of turns in the
secondary.
If Vp and Vs be the input and output voltage respectively, Np
and Ns be the number of turns on the primary and secondary,
then
T = = (1)
T = is knows as transformer ration.
If T>1, then Vs > Vp. The output voltage is greater than
the inout voltage. Such as transformer is known as step-up
transformer.
For a step-up transformer, Vs > Vp. Therefore, Is > Ip.
Then step-up transformer steps down the current.
For a step-down transformer, Vs < Vp. Therefore, Is> Ip.
Then step-down transformer step up the current.
However, in a transformer there are always power losses and
output power is less than the input power.
The efficiency of transformer is the ratio of output power to
the input power.
17.
a. It could not explain the spectra of complex atoms having more
than one electron.
b. It does not give an idea about the distribution of electron
in an atom.
c. This model could not account for the wave nature and
electron.
d. It does not give any idea about the relative intensity of
spectral lines.
18. Rectification:
The process of converting an alternating current into a direct
current is called Rectification.
Full wave rectifier:
A rectifier which rectifies both half cycle of the AC input is
called full wave rectifier.
Construction:
A Full wave rectifier can be constructed with two diodes D1 and
D2 centre tap transformer, load resistance RLand ACinput as shown
in fig.
In centre tap transformer, the secondary coil is wound into two
equal parts. Voltage at A and B with respect ti centre tap C are
out of phase with respect to each other.
Working:
During the positive half cycles of AC input, diode D1 is forward
biased and diode D2 is release biased. The diode D2 will not
conduct and the current flows through the load resistance RL is due
to D1
Similarly, during negative half cycle of AC input, diode D2 is
forward biased and D1 is reverse biased. Diode D1 will not conduct
and the current flows through load resistance R2 due to D2
Hence, current flows through the load resistance during both the
half cycles and will be the same direction.
Therefore, using Full wave rectifier, the output is continuous
but pulsating as shown in figure.
V
-Vinput++AC input P n
Output- A D1 --
RL P C s
+++ B V
D2 o t output
The efficiency of the full wave rectifier is
=
rf is diode forward resistance
SECTION C
19. Doppler effect:The apparent change in frequency of sound
observed due to relative motion between the observer and the source
of sound is called Doppler effect.
Source is in motion, observer and medium at rest:
Let S and O be the positions of the source and the observer
respectively.
Let n = frequency of sound waves emitted by source
V = velocity of sound waves
When the source is at rest, it will emit n wave in one
second.
So nwaves occupy a length V in one second.
VImplies wavelength of waves = =
OS
V - VsVs
OS1S
If the source moves with velocity Vs towards the observer it
reaches a point S1 after one second.
No n waves are present in a length of V-VS
Implies New wavelength = 1 =
Implies Apparent frequency = n1 = = () n
Since V > (V-Vs), n1 > n
When source moves towards a stationary observes, the apparent
frequency of sound waves will be greater than the actual
frequency.
If the source moves away from the observer, Vs is replaced by
Vs.
Implies Apparent frequency = n1= ( ) n
Since V < (V + Vs), n1 < n
When source moves away from stationary observer the apparent
frequency is less than the actual frequency.
20. Torque on a current loop (or) coil uniform magnetic
field:
Consider a rectangular loop placed such that the uniform
magnetic field B is in the plane of the loop. The field exerts no
force on the two arms AD and BC of the loop. It is perpendicular to
the arm. AB of the loop and exerts a force F1 on it which is
directed into the plane of the loop.
Its magnitude is F1 = lbB
Similarly it exerts a force F2 on arm CD and F2 is directed out
of the plane of the paper.
F2 = lbB = F1
Thus, the net force on the loop is zero. There is a torque on
the loop due to the pair of forces F1 and F2. This torque on the
loop tends to rotate it anti-clockwise and is given by
= F1 ( ) + F2 ( ) = lbB ( ) + lbB ( ) = I (ab)B = IAB.
F2
m
F1
Where A = ab is the area of the rectangle.
When the plane of the loop is not analog the magnetic field: but
makes an angle with it, we take the angle between the field and the
normal to the coil to be angle
The force on arms AB and CD are F1 and F2 and are equal and
opposite, with magnitude.
F1 = F2 = IbB. These two forces constitute a couple and
magnitude of the torque on the loop is
= F1 ( )sin + F2 ( ) sin = Iab sin = IAB sin
The moving coil galvanometer:
Principle: when a coil carrying current is placed in a magnetic
field, it experiences a torque and hence deflects.
Descriptions:The galvanometer consists of a coil, with many
turns, free to rotate about a fixed axis in a uniform radial
magnetic field. There is a cylindrical soft iron core which not
only makes the field radial but also increases the strength of the
magnetic field.
Scale
Coil Soft iron core Pointer
Permanent magnet
N
S
Uniform magnetic field
Theory:
When a current flows through the coil, a torque acts on it.
The torque is given by = NIAB
Since, the field is radial, we have taken sin =1, in the above
expression for the torque. The deflecting torque NIAB tends to
rotate tge coil. A spring provides a rotating torque K, that
balances the deflecting torque NIAB. Resulting in a steady angular
deflection .
In equilibriumK = NIAB
Where K is the torsional constant of the spring. i.e. the
restoring torque per unit twist. The deflection is indicated on the
scale by a pointer attached to the spring.
We have = ( ) I
21. Principle: A nuclear reactor is a device which works on the
principe if controlled chain reaction. It is also called an atomic
pile figure shoes the schematic diagram of a nuclear reactor. The
core of the nuclear reactor is the place where nuclear fission
process takes place.
Coolant
Control RodsHeat exchanger (steam generator)Steam to Turbine
Water from Condensor
Reflector
The essential components of a nuclear reactor are,
(1) Fuel
(2) Moderator
(3) Control rods
(4) Radiation shielding
(5) Coolant
(1) Fuel: The fissionable materials used in the reactors is
called nuclear fuel. The nuclear fuel is taken in the form of rods
and sealed in aluminium cylinders.
Ex: Enriched uranium, U235, enriched plutonium or U233 etc.
(2) Moderator:Moderator is a substance which slow down the fast
moving neutrons produces during the nuclear fission process. The
average energy of neutrons released in the fission process is 2Mev.
They are slow down to thermal neutrons. (0.025eV) by moderator.
Ex: Heavy water, graphite, Hydrocarbon plastics etc.
(3) Control rods:The fission rate in the reactor is controlled
by using the neutron absorbing materials.
Ex: Cadmium and Boron rods
(4) Shielding:During fission reaction beta () and gamma ()
radiation are emitted along with neutrons. Suitable shielding such
as steel, lead and concrete walls are provided around the reactor
to absorb and reduce the intensity of radiation.
(5) Coolant: the heat generated in fuel elements is removed by
using a suitable coolant to flow around them. The coolant used are
water at high pressures, molten sodium, etc.
Working:
Uranium fuel rods are placed in the aluminium cylinders, which
are separated by some distance. The graphite moderator is placed in
between the fuel cylinders.
The control rods are kept in the holes of the graphite block.
When a few U235 nuclei undergo fission, fast neutrons are
liberated.
These neutrons pass through graphite moderator and loose their
energies to be comes thermal neutrons. These thermal neutrons
participate in further fission process.
By proper adjustment is used for heating the coolan, heat is
transformed to water and steam isproduced. This steam is used to
run the turbine. This turbine is used to drive a generator to
produce electricity.
