PHYSICS

Single correct answer type:

1. A ball is released from certain height which losses 50% of its kinetic energy on

striking the ground, it will attain a height again

(A)

th of initial height

(B)

th of initial height

(C)

th of initial height

(D) None of the above

Solution: (B)

Ratio of heights

of the initial height.

2. If applied torque on a system is zero, i.e., , then for that system.

(A)

(B)

(C)

(D)

Solution: (B)

moment of inertia

angular acceleration

If

But

3. A steel wire of 1 m long and cross section area is hanged from rigid end

when weight of 1 kg is hang from it, then change in length will be

(Young’s coefficient for wire ⁄ )

(A) 0.5 mm

(B) 0.25 mm

(C) 0.05 mm

(D) 5 mm

Solution: (C)

Young’s coefficient of elasticity

Substituting the values, we get

4. When plate voltage in diode value is increased from 100V to 150V. Then, plate

increased from 100V to 150v. Then, plate increases from 7.5 mA to 12 mA, then

dynamic plate resistance will be

(A)

(B)

(C)

(D)

Solution: (D)

Plate resistance

( )

5. If the sun rays are incidenting at angle and intensity is . If the sun rays are

made incident at angle, then what will be the intensity?

(A)

√

(B) √

(C)

(D)

Solution: (B)

Ratio intensities

√

6. The reason of current flow in p-n junction in forward bias is

(A) Drifting of charge carriers

(B) Drifting of minority charge carriers

(C) Diffusion of charge carriers

(D) All of the above

Solution: (C)

Due to diffusion of charge carriers current flows throw in p-n junction

7. A charged particle is accelerated by a potential of 200V. If its velocity is

⁄ , then value of ⁄ for that particle is

(A)

(B)

(C)

(D)

Solution: (C)

If electron is accelerated by voltage V, then its kinetic energy

( )

8. When an open organ is dipped in water upto half of its height, then its frequency

will become

(A) half

(B) double

(C) remain same

(D) four time

Solution: (C)

Frequency of open organ pipe is double than that of closed pipe.

If frequency of open pipe = n

Frequency of closed pipe

On inserting an open pipe into water upto half of its height, it will behave like a

closed pipe of half length and frequency is inversely proportional to the length of

air column.

Hence, frequency of closed pipe will become double

9. A sound source producing waves frequency 300 Hz and wavelength 1m observe

is stationary, while source is going away with the velocity 30 m/s, then apparent

frequency heared by the observer is

(A) 270 Hz

(B) 273 Hz

(C) 383 Hz

(D) 300 Hz

Solution: (B)

Apparent frequency (

)

velocity of sound,

velocity of source

(

)

10. A particle moves towards east for 2s with velocity 15 m/s and move towards

north for 8 s with velocity 5 m/s. Then, average velocity of the particle is

(A) 1 m/s

(B) 5 m/s

(C) 7 m/s

(D) 10 m/s

Solution: (B)

Distance covered towards east

Distance covered towards north

Total displacement

√

Average velocity

⁄

11. Relation between wavelength of photon and electron of same energy is

(A)

(B)

(C)

(D)

Solution: (A)

Wavelength

√

√

Mass of photon is less than that of electron

Wavelength of photon is greater than that of electron

12. Match the following.

Angular momentum

1. [ ]

Torque 2. [ ] Gravitational

constant 3. [ ]

Tension 4. [ ] (A)

(B)

(C)

(D)

Solution: (B)

Dimension of torque [ ]

Dimension of angular momentum [ ]

Relation is right.

13. If we increase kinetic energy of a body 300%, then percent increase in its

momentum is

(A) 50%

(B) 300%

(C) 100%

(D) 150%

Solution: (C)

√

√

√

14. Change in acceleration due to gravity is same upto a height h from each other

the earth surface and below depth , then relation between x and h is (h and

)

(A)

(B)

(C)

(D)

Solution: (B)

Variation in g at a height h from the earth surface (

)

Variation in a g at a depth x below the earth surface (

)

But variation are same

(

) (

)

15. A Mass of 1 kg is suspended from a spring of force constant 400 N, executing

SHM total energy of the body is 2J,then maximum acceleration of the spring will

be

(A) ⁄

(B) ⁄

(C) ⁄

(D) 400 ⁄

Solution: (B)

√

√

Frequency

Total energy

Acceleration

⁄

16. Two capacitors of capacities and are charged upto the potential and

then condition for not flowing the charge between on connected them in

parallel is

(A)

(B)

(C)

(D)

Solution: (B)

If charge on both the capacitors is same, then transfer of energy does not take

place.

It is the required condition.

17. Find equivalent resistance between X and Y

(A) R

(B)

(C)

(D)

Solution: (A)

The given circuit can be shown in the following way. No, current will be flown in

the middle resistance.

Equivalent resistance of R and

Total resistance

18. Vibrations of rope tied by two rigid ends shown by equation , then

minimum length of the rope will be

(A) 1m

(B)

(C)

(D)

Solution: (B)

Equation of vibration

⁄

Comparing this equation with

Minimum length of string

19. If we change the value of R, then

(A) voltage does not change on L

(B) voltage does not change on LC combination

(C) voltage does not change on C

(D) voltage changes on LC combination

Solution: (D)

If we change the value of R, then voltage on LC combination changes.

20. If , then electric field at a point will be proportional to

(A)

(B)

(C)

(D)

Solution: (D)

Electric field

21. Electric field at point 20 cm away from the centre of dielectric sphere is 100 V/m,

radius of spheres is 10 cm, then the value of electric field at a distance 3 cm from

the centre is

(A) ⁄

(B) ⁄

(C) ⁄

(D) 0

Solution: (D)

Inside a dielectric sphere, electric field is zero.

22. 50 g ice at in insulator vessel, 50 g water of is mixed in t, then final

temperature of the mixture is (neglect the heat loss)

(A)

(B)

(C)

(D) Above

Solution: (A)

According to galvanometer principle.

Heat given = Heat taken

( ) ( )

( ) ( )

23. Real power consumption in a circuit s least when it contains.

(A) High R, low L

(B) High R, high L

(C) Low R, high L

(D) High R, low C

Solution: (C)

Power consumption

Where, is power factor.

For to be minimum, R should be minimum and Z should be higher. So,

higher (impedance), L (inductance) should be high.

24. Linear density of a string of is ⁄ and wave equation is

( ). Find, the tension in the string where, x in metre and t in

second.

(A) 0.12 N

(B) 0.21 N

(C) 1.2 N

(D) 0.012 N

Solution: (A)

Mass per unit length ⁄

( )

Comparing with (

)

We know that

25. Magnetic field at point O will be

(A)

(B)

(C)

(

)

(D)

(

)

Solution: (A)

Magnetic field at the centre of circular loop

interior.

26. If prim angle distance between screen and prism ( ) ,

distance between prism and source , then in Fresnel

biprism find the value of (fringe width).

(A)

(B)

(C)

(D)

Solution: (B)

, we know that ( )

( )

( )

Fringe width

27. According to Bohr’s model of hydrogen atom, relation between principal quantum

number n and radius of stable orbit is

(A)

(B)

(C)

(D)

Solution: (D)

According to Bohr’s model, relation between principal quantum number (n) and

radius of stable orbit ® are related as

According to Bohr’s model, relation between principle quantum number (n) and

radius of stable orbit (r) are related as

28. An observer is approaching with velocity towards a light source. If the velocity

of light is c, then velocity of light with respect to observer will be

(A)

(B)

(C)

(D) √ ⁄

Solution: (C)

Observer and light are moving towards each other, so relative velocity is .

29. Magnetic field of the earth is . A magnet is vibrating 5 oscillations per

min then the dippreciation required in the magnetic field of the earth of increase

time period upto 10 oscillations per minute is

(A) 2.25 g

(B) 0.6 g

(C) 0.9 g

(D) 0.12 g

Solution: (A)

We know that

√

√

√

√

Depreciation in field

30. Work function of a metal is , then its threshold wavelength will be

(A)

(B)

(C)

(D)

Solution: (D)

Work function

31. Remaining quantity (in %) of radioactive element after 5 half lives is

(A) 4.125%

(B) 3.125%

(C) 31.1%

(D) 42.125%

Solution: (B)

Remaining quantity

(

)

(

)

In percentage,

32. A engine pumps up 100 kg of water through a height of m in s. Given that, the

efficiency of engine is 60 %. If , the power of this engine is

(A) 3.3 kW

(B) 0.33 kW

(C) 0.033 kW

(D) 33 kW

Solution: (A)

Efficiency of engine

Thus, power ⁄

Given, and

Hence,

33. The angular amplitude of a simple pendulum is . The maximum tension in its

string will be

(A) ( )

(B) ( )

(C) ( )

(D) ( )

Solution: (D)

The simple pendulum at angular amplitude is shown in the figure.

…(i)

When, bob of pendulum comes from A to B, it coves a vertical distance h.

( ) …(ii)

Also, during A and B, potential energy of bob converts into kinetic energy

√ …(iii)

Thus, using equations. (i), (ii) and (iii) we obtain

( )

*

+

(By using binomial theorem)

( )

34. If the electric flux entering and leaving an enclosed surface respectively are ,

and , the electric charge inside the surface will be

(A)

(B)

(C)

(D) ( )

Solution: (D)

According to Gauss theorem “the net electric flux through any closed surface is

equal to the net charge inside the surface divided by ”.

Therefore ,

Let be the charge, due to which flux is entering the surface.

Or

Let be the charge, due to which flux is entering the surface.

Or

So, electric charge inside the surface

( )

35. During an adiabatic process, the pressure of a gas is found to be proportional to

the cube of absolute temperature. The ratio

for the gas is

(A)

(B)

(C)

(D)

Solution: (D)

Given that

Or …(i)

Also for adiabatic process,

But ( )

Or

(

)

Or ( )⁄ …(ii))

Equating equations. (i) and (ii), we get

Or

Or

Or

36. Three points charges and are placed at points (

) ( ) and ( ), respectively. The magnitude

and direction of the electric dipole moment vector of this charge assembly are

(A) √

(B) √ along the line joining points ( ) and ( ) (C) along the line joining points ( ) and ( )

(D) √ along + -direction

Solution: (B)

O is the origin at which charge is placed. The system is equivalent to two

dipoles along and -directions respectively. The dipole moments of two dipoles

are shown in figures.

The resultant dipole moment will be directed along OP where ( ). The

magnitude of resultant dipole moment is

√ √( ) ( ) √

37. A block B is pushed momentarily along a horizontal surface with an initial velocity

. If is the coefficient of vlicling friction between B and the surface, block B will

come to rest after a time

(A)

(B)

(C)

(D)

Solution: (A)

Block will come to rest, if force applied on it. It will vanish due to frictional force

acting between block B and surface, i.e.,

Force applied = Frictional force

i.e.,

or (

) or

38. To get three images of a single object, we should have two plane mirrors at an

angle of

(A)

(B)

(C)

(D)

Solution: (B)

39. A particle of mass M and charge moving with velocity describes a circular

path of radius when subjected to a uniform transverse magnetic field of

induction . The work done by the field, when the particle completes one full

circle, is

(A) (

)

(B)

(C)

(D)

Solution: (B)

When particle describes circular path in a magnetic field, its velocity is always

perpendicular to the magnetic force?

Power

Hence,

But

Hence, work done (everywhere)

40. A particle of mas 100 g is thrown vertically upward with a speed of ⁄ . The

work done by the force of gravity during the time the particle up is

(A) (B)

(C)

(D)

Solution: (B)

The height (h) transverse by particle while going up is

Work done by gravity force

(angle between force and displacement is )