Dropper Test.docx

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Sombir Classes By Er. Sombir Ahlawat

Test : EMI + Centre Mass + Work power

Ahlawat Tower, Near HDFC and PNB Bank, Sonepat road, Rohtak Contact No. 8930818212 1

1) According to faraday’s law, the total charge induced in a conductor, i.e., moved in magnetic field

depend upon:

(a) initial magnetic flux (b) final magnetic flux

(c) rate of change of magnetic flux (d) change in magnetic flux

2) Flux (in weber) in a closed circuit of resistance 10 ohm varies with time t (in sec) according to

equation 26 5 1t t . What is magnitude of the induced current at t = 0.25s?

(a) 1.2A (b) 0.8A (c) 0.6A (d) 0.2A

3) A conducting square loop of side L and resistance R moves in its plane with a uniform velocity v

perpendicular to one of its sides. A magnetic induction B, constant in time and space pointing

perpendicular and into the plane of the loop everywhere. The current induced in the loop is:

(a) BvL/R, clockwise

(b) BvL/R, anticlockwise

(c) 2BvL/R, anticlockwise

(d) Zero

4) A short-circuited coil is placed in a time varying magnetic field. Electrical power is dissipated due to the

current induced in the coil. If the number of turns were to be quadrupled and the wire radius halved, the

electrical power dissipated would be:

(a) halved (b) the same

(c) doubled (d) quadrupled

5) A rectangular coil ABCD is rotated anticlockwise with a uniform angular velocity about an axis as shown.

The axis of rotation of the coil as well as the magnetic filed B are horizontal. The induced emf in the coil

would be minimum when

(a) the plane of coil is horizontal

(b) the plane of the coil is vertical

(c) the plane of the coil makes an angle 450

with the direction of the magnetic field

(d) the plane of the coil makes an angle of 300 with the field

6) Magnetic flux through a circuit of resistance R changes by an amount in time t . Total quantity of

electric charge Q that passes any point in the circuit during the time t is represented by:

1( ) ( )

( ) ( )

a Q b Q R t R

c Q d Q Rt t

7) Current through coil increases from zero to 6A in 0.3 sec and an induced emf of 30V is produced.

Inductance of the coil is:

V

BA

B

C

D






(a) 2.5H (b) 5H

(c) 1.5H (d) 2H

8) When a battery is connected across a series combination of self inductance L and resistance R, the variation

of current ‘I’ with time ‘t’ is best represented by:

9) A small piece of metal wire is dragged across the gap between the poles of a magnet in 0.4sec. if the

change in magnetic flux is 8×10-4wb, emf induced in the wire is:

(a) 8×10-3V (b) 6×10-3V (c) 4×10-3V (d) 2×10-3V

10) If a coil of 40 turns and area 4cm2 is suddenly removed from a magnetic field, it is observed that a charge

of 2×10-4C flows into the coil. If the resistance of the coil is 80 ohm, the magnetic flux density in Wb/m 2 is:

(a) 0.5 (b) 1 (c) 1.5 (d) 2

11) If a radius of coil is changing at the rate 10-2 units in a normal magnetic field 10 -3units, the induced emf is

1μV. What is final radius of coil?

(a) 1.6cm (b) 16cm (c) 12cm (d) 1.2cm

12) A long solenoid has 500 turns. When a current of 2 ampere is passed through it, the resulting magnetic flux

linked with each turn of solenoid is 4×10 -3Wb. The self-inductance of the solenoid is :

(a) 1 henry (b) 4 henry (c) 2.5 henry (d) 2 henry

13) A circular disc of radius 0.2 metre is placed in uniform magnetic field of induction2

1( )

wb

m in such a way

that its axis makes an angle 600 with B. the magnetic flux linked with the disc is:

(a) 0.08Wb (b) 0.01Wb (c) 0.02Wb (d) 0.06Wb

14) When a magnet M is pushed in and out of a circular coil C connected to a very sensitive galvanometer G as

shown, with frequency f:

(a) constant deflection will be observed in the galvanometer

(b) visible small variation will be observed in the voltmeter i f ‘f’ is about 50Hz.

(c) Oscillation in the deflection will be seen clearly when f = 1 or 2 Hz.

(d) No variation in the deflection will be seen even when f = 1 or 2 Hz.

I

t

t

I

C

NS

M

G






15) A rectangular coil of 300 turns has an area 25cm×10cm. the coil rotates with a speed of 50cps in a uniform

magnetic field of 4×10-2T about an axis perpendicular to the field. The value of peak induced emf in it is:

(a) 0.3πvolt (b) 3π volt (c) 30π volt (d) 3000π volt

16) A metallic square loop ABCD is moving in its own plane with velocity v in a uniform magnetic field

perpendicular to its plane as shown. An electric field is induced:

(a) in AD, but not in BC

(b) in BC, but not in AD

(c) neither in AD nor in BC

(d) in both AD and BC

17) The variation of induced emf (e) with time (t) in a coil if a short bar magnet is moved along its axis with a

constant velocity is best represented as:

(a) (b)

(c) (d)

18) Two coaxial solenoids are made by winding thin insulated wire over a pipe of cross sectional area A =

10cm2 and length = 20cm. if one of the solenoids has 300 turns and the other 400 turns, their mutual

inductance is (μ0 = 4π×10-7TmA-1)

(a) 2.4π×10-4H (b) 2.4π×10-5H

(c) 4.8π×10-4H (d) 4.8π×10-5H

19) A straight conductor with its length in the east-west directions fall under gravity while sliding on a fixed

conducting frame. Due to earth’s magnetic field,

(a) induced emf develops with the east end at higher

potential than the west end and induced current in the

conductor passes from west to east

(b) induced emf develops with the east end at lower

potential than the west end and induced current in the

conductor passes from west to east

(c) induced emf develops with the west-end at higher potential than the east-end and induced current passes

from west to east

emf

Time

emf

Time

emf

Time

emf

Time

A B

CD






(d) sense of induced emf and induced current is unpredictable

20) Figure shows a square loop of side ‘a’ rotating about the given axe in a uniform magnetic field such that the

field is perpendicular to the axes in both the cases. Angular speed of rotation is both cases being the same,

(a) induced emf is more in (a) than in (b)

(b) induced emf is more in (b) than in (a)

(c) induced emf is the two cases are equal and nn-zero (a) (b)

(d) induced emf in the two cases are equal and zero

21) Figure shows a magnet suspended at the lower end of a spring and with its length along the axis of a fixed

circular conducting coil. The magnet is made to oscillate. Deflection in the galvanometer is:

(a) minimum when the magnet is at mean position

(b)maximum when the magnet is at mean position

(c) zero when the magnet is at mean position

(d) maximum when the magnet is at extreme position

22) An infinitely long cylinder is kept parallel to a uniform magnetic field B directed along positive Z-

axis. The direction of the induced current on the surface of cylinder as seen from the Z-axis will be:

(a) clockwise of the +ve Z-axis (b) anticlockwise of the +ve Z-axis

(c) zero (d) along the magnetic field

23) A conducting circular loop is placed in a uniform magnetic field 0.04T with its plane perpendicular to the

magnetic field. The radius of the loop starts sinking at 2mm/s. the induced emf in the loop when the radius

is 2cm is:

(a) 1.6πμV (b) 3.2πμV (c) 4.8πμV (d) 0.8πμV

24) A rectangular, a square, a circular and an elliptical loop, all in the x-y plane are moving out of a uniform

magnetic field with a constant velocity ˆV Vi . The magnetic field is directed along the negative Z-axis

direction. The induced emf, during the passage of these loops, out of the field region will not remain

constant for:

(a) any of four loops (b) the rectangular, circular and elliptical loops

(c) circular and elliptical loops (d) only the elliptical loop

25) A simple pendulum is released from A as shown. If m and l represents the mass of bob and the

length of pendulum respectively, the gain in kinetic energy at B is :

(a)mgl/2

(b)mgl/√2

(c)√3mgl/2

(d)2mgl/√3

26) An engine pumps up 100kg of water through a height of 10m in 5s. Given that, the efficiency of engine is

60%. If g = 10m/s2, the power of this engine is:

S

N

G

300

B






(a) 3.3kW (b) 0.33kW (c) 0.033kW (d) 33kW

27) In figure, a block of mass 4kg falls on a spring from a height of 15cm. if spring constant of the

spring is 2000N/m, maximum compression on the spring will be: ( g = 10m/s 2):

(a) 14cm (b) 18.2cm (c) 12.6cm (d) 10cm

28) Two blocks are connected by a spring, the blocks are placed on a horizontal rough surface with ‘µ’

as the coefficient of friction between the blocks and the surface. Minimum horizontal force on M 1 so as to

move M2 is :

(a) µM2g (b) µ(M1-M2)g (c) µ(M1+M2)g (d) µ/2(2M1+M2)g

29) A particle of mass m is moving in a circular path of constant radius r such that its centripetal acceleration ac

is varying with time t as ac = k 2rt2 where k is a constant. The power delivered to the particle by the force

acting on it is:

(a) 2 πmk 2r 2t (b) mk 2r 2t (c) mk 4r 2t5/3 (d) zero

30) The space craft of mass M move with a velocity V in a free space at first, then it explodes breaking into

pieces. If after explosion a piece of mass m comes to rest, the other piece of space craft will have a

velocity:

(a)MV/(M-m) (b)MV/(M+m) (c)mV/(M-m) (d)mV/(M+m)

31) A body of mass 1kg initially at rest, explodes and breaks into three fragments of masses in the ratio 1:1:3.

The two pieces of equal masses fly off perpendicular to each other with a speed of 15m/s each. The speed

of heavier fragment is:

(a)5/√2m/s (b)45m/s (c)5m/s (d)15m/s

32) A body of mass M at rest explodes into three pieces, two of mass (M/4) each are thrown off in

perpendicular directions with velocities of 3m/s and 4m/s respectively. The third piece will be thrown off

with a velocity of:

(a)1.5m/s (b)2m/s (c)2.5m/s (d)3m/s

33) Two skaters A and B of masses 50kg and 70kg respectively stand facing each other 6m apart. Then they

pull on a rope stretched between them. How far has each moved when they meet?

(a)both have moved 3m (b)A moves 2.5m and B 2.5m

(c)A moves 3.5m and B 2.5m (d)A moves 2m and B 4m

15cm

M1 M2

F K






34) A man weighing 80kg is standing on a trolley weighing 320kg. the trolley is resting on a frictionless

horizontal rails. If the man starts walking on the trolley along the arils at the speed 1m/s, then after 4s his

displacement relative to the ground will be:

(a)5m (b)4.8m (c)3.2m (d)3m

35) Two particles of masses M and 2M are at a distance D apart. Under their mutual gravitational force the start

moving towards each other. The acceleration of their centre of mass when they are D/2 apart is:

(a)2GM/D2 (b)4GM/D2 (c)8GM/D2 (d) Zero

36) A bomb traveling in a parabolic path under the effect of gravity, explodes in the mid air. The centre of mass

fragments will:

(a)move vertically upwards and then downwards (b)move in vertically downwards

(c)move in irregular path (d)move in parabolic path the unexploded bomb will have traveled

37) An object of mass ‘2m’ is projected with a velocity v at an angle θ with the horizontal. At the highest point

of its path, it explodes into two fragments of equal masses such that speed of one of the fragments

immediately after the explosion is zero. Distance from the point of projection at which the centre of mass m

hits the horizontal is:

(a)2 sinv

g

(b)

2 sin

2

v

g

(c)2 sin2v

g

(d)

sin

2

v

g

38) A 400kg boat is 6m long. It is floating in still water and is at rest. A person of mass 80kg move from one

end of the boat to the other. Displacement of the boat relative to water is:

(a)1m in a direction opposite to displacement of person

(b)0.5m in the direction opposite to displacement of person

(c)1.5m in the direction opposite to displacement of person

(d)1.5m in the direction of displacement of person

39) A person of mass 80kg is standing on a boat of 320kg which at rest in still water. The person is initially

12m from the shore. The person walks on boat for 6sec with a constant speed 1m/s towards the shore and

then stops. Distance of the person from the shore is finally:

(a)4.8m (b)6.4m (c)7.2m (d)8.2m

40) A 10kg shell, initially at rest, explodes into three fragments of masses 4kg, 4kg and 2kg. if the two

fragments of equal masses moves towards north and towards west with equal speed 4m/s, velocity of the

2kg fragment will be:

(a)8m/s along north-west (b)8/√2m/s along the south-west

(c)8m/s along the north-east (d)8√2m/s along south-east

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Dropper Test.docx