VELAMMAL BODHI CAMPUS, KOLAPAKKAM

Work sheet chapter6

CLASS 12 - PHYSICS

Section A 11) If two coils of inductancesL1 and L2 are linked such that
their mutual inductance is M, then the maximum value of M
1) Two coils have a mutual inductance 0.005 H. The current is
changes in the first coil according to equation I = I0 sin Ωt ,
where I0 = 10 A and ω = 100 π rad s - 1 . The maximum a) L1 - L2
value of emf in the second coil is b) L1 + L2
a) 12π b) 2π c) √1 × L2
L
c) 5π d) 6π d) L1 L2
2) A small coil of radius r is placed at the centre of a large 12) Two inductors each of inductance L are joined in parallel.
coil of radius R, where R » r. The two coils are coplanar. What is their equivalent inductance?
The mutual induction of the coils is proportional to a) 2 L b) Zero
a) Rr2 b) Rr c) L d) L2
c) rR d) Rr 2
2 2
13) A 10m long horizontal wire extends from North - East to
3) An inductor may store energy in South - West. It is falling with a speed of 5.0 ms - 1 at right
angles to the horizontal component of the earth’s magnetic
a) Its magnetic field field of 0.3 × 10 - 4 Wb/m2 . The value of the induced
b) Its electric field emf in wire is
c) Both in electric and magnetic fields a) 2.5× 10 - 3 V b) 1.1× 10 - 3 V
d) Its coils c) 0.3× 10 - 3 V d) 1.5× 10 - 3 V
4) An ac generator consists of 8 turns of wire, each of area A 14) A 100 mH coil carries a current of 1 A. Energy stored in
= 0.0900 m2 , and the total resistance of the wire is 12.0Ω . the form of magnetic field is
The loop rotates in a 0.500 T magnetic field at a constant a) 0 · 1 J b) 0 · 5J
frequency of 60.0 Hz. Maximum induced emf is c) 0 · 05 J d) 1 J
a) 126 V b) 116 V
c) 106 V d) 136 V 15) For a coil having L = 2× 103 H, current flows at the rate
of 10 - 3 A/s. The emf induced is:
5) A pair of adjacent coils has a mutual inductance of 1.5 H. a) 3 V b) 2 V
If the current in one coil changes from 0 to 20 A in 0.5 s, c) 4 V d) 1 V
change of flux linkage with the other coil is
16) A conducting circular loop is placed in a uniform magnetic
a) 45 Wb b) 35 Wb
field, B = 0.025 T with its plane perpendicular to the loop.
c) 30 Wb d) 40 Wb
The radius of the loop is made to shrink at a constant rate
6) An inductor of inductance 10 H is connected in series with a of 1 mm s - 1 . The induced emf when the radius is 2 cm,
resistance R = 6 ohm. A 12 - volt battery is connected for is
a long time. When the circuit is switched off, the induced
a) 2µV
emf in the inductor, if current reduces to zero in 10 ms, is
b) πµV
a) 2000 V b) 1000 V
c) 2πµV
c) 4000 V d) 3000 V
d) π2 µV
7) Assume that a motor in which the coils have a total resistance
17) In the circuit shown in the following figure E = 10 V, R1
of10Ω is supplied by a voltage of 120 V. When the motor
= 2 ohm, R2 = 3 ohm and R3 = 6 ohm and L = 5 henry.
is running at its maximum speed, the back emf is 70 V.
The current I1 just after releasing the switch is:
Current in the coils when the motor is turned on and when
it has reached maximum speed are
a) 16 A, 5 A b) 14 A, 5 A
c) 12 A, 4 A d) 12 A, 5 A
8) A horizontal ring of radius r spins about it’s axis with an
a) ( 10
5 )amp b) Zero
angular velocityω in a uniform magnetic field of magnitude
c) ( 10
4 )amp d) ( 10
12 )amp
B. Emf induced in the ring is
a) r2 ωB b) πr2 ωB 18) The working of a dynamo is based on the principle of
c) πr ωB d) Zero
3
a) Chemical effect of current
9) A coil of resistance 400Ω is placed in a magnetic field. If b) Electromagnetic induction
the magnetic flux ϕ (Wb) linked with the coil varies with c) Magnetic effect of current
times t (sec) as ϕ = 50t2 + 4, the current in the coil at t = d) Heating effect of current
2 sec is: 19) In a coil of self - induction 5 H, the rate of change of
a) 0.1 A b) 1 A
current is 2 A s - 1
. Then, e.m.f. induced in the coil is
c) 0.5 A d) 2 A
a) 10 V b) - 10 V
10) Suppose the number of turns in a coil be tripled, the value c) - 5 V d) 5 V
of magnetic flux linked with it
20) The current in a self - inductance L = 40 mH is to be
a) None of these b) Becomes 13
increased uniformly from 1 A to 11 A in 4 milliseconds.
c) Remains unchanged d) Is tripled
The emf induced in the inductor during the process is:
 a) 440 V b) 100 V a) 2 b) 8
c) 40 V d) 0.4 V c) 4 d) 6
21) Current in a circuit falls from 5 A to 0 A in 0.1 s. If an 29) As shown in the figure, two vertical conducting rails sepa-
average emf of 200 V is induced, the self - inductance of rated by a distance of 1.0 m are placed parallel to z - axis.
the circuit is At z = 0, a capacitor of 0.15 F is connected between the
a) 5H b) 4H rails and a metal rod of mass 100 gm placed across the rails
c) 2H d) 3H slides down along the rails. If a constant magnetic field of
22) What is self inductance of a coil which produces 5 V, when 2.0 T exists perpendicular to the plane of the rails, what is
current in it changes from 3 A to 2 A in one millisecond? the acceleration of the rod? (Take g = 9.8 11s, what is
a) 5 mH b) 50 mH m/s2 )
c) 5000 H d) 5 H
23) A long solenoid has 800 turns per meter. A current of 1.6
A flows through it. The magnetic induction at the end of a) 0 b) 9.8 m/s2
solenoid on its axis is c) 2.5 m/s2 d) 1.4 m/s2
a) 16.0 × 10−4 T 30) A 50 cm long bar AB is moved with a speed of 4 ms - 1

b) 8.04 × 10−4 T in a magnetic field B=0.01 T as shown in the fig.

c) 4.0 × 10−4 T The emf generated is
d) 2.0 × 10−4 T
24) Two inductors of inductance L each are connected in se-
ries with opposite magnetic fluxes. What is the resultant
inductance?
a) L b) Zero
c) 2 L d) 3 L a) 0.03 V b) 0.02 V
c) 0.04 V d) 0.01 V
25) The phase difference between the flux linked with a Coil ro-
tating in a uniform magnetic field and induced emf produced 31) Assertion (A): A conducting rod is moving in a uniform
in it is: magnetic field such that the length of the rod, its velocity
a) −π
6 b) π2 and the magnetic field are mutually perpendicular, then, an
c) 3
π
d) π emf will be induced between the ends of the rod.
26) A metallic rod of 1 m length is rotated with a frequency of Reason (R): As the rod moves as stated above, free electrons
50 rev/s about an axis passing through the centre point O. in it will experience magnetic force towards an end of the
Other end of the metallic rod slides on a Metallic ring. A conductor.
constant and uniform magnetic field of 2 T parallel to the a) Both A and R are true and R is the correct explanation
axis is present everywhere. What is the emf between the of A.
centre and the metallic ring? b) Both A and R are true but R is not the correct expla-
nation of A.
c) A is true but R is false.
d) A is false but R is true.
32) Assertion (A):The bar magnet falling vertically along the axis
of the horizontal coil will be having an acceleration of less
than g.
a) 240 V b) 300 V
Reason (R): Clockwise current is induced in the coil.
c) 220 V d) 314 V
27) If the vertical component of earth’s magnetic field be 6×
10 - 5 Wbm2 , then what will be the induced potential differ-
ence produced between the rails of a meter - gauge when a
train is running on them with a speed of 36 km/h?

a) Both A and R are true and R is the correct explanation

of A.
b) Both A and R are true but R is not the correct expla-
nation of A.
a) 3 × 10−4 V c) A is true but R is false.
b) 9 × 10−4 V d) A is false but R is true.
c) 2 × 104 V
d) 6 × 104 V 33) Assertion (A):Lenz’s law violates the principle of conserva-
tion of energy.
28) In a coil of resistance 10Ω , the induced current developed Reason (R): Induced emf always opposes the change in mag-
by changing magnetic flux through it, is shown in the figure netic flux responsible for its production.
as a function of time. The magnitude of change in flux
through the coil in weber is: a) Both A and R are true and R is the correct explanation
of A.
b) Both A and R are true but R is not the correct expla-
nation of A.
c) A is true but R is false.
d) A is false but R is true.
34) Assertion (A):Figure shows a horizontal solenoid connected b) Both A and R are true but R is not the correct expla-
to a battery and a switch. A copper ring is placed on a nation of A.
smooth surface, the axis of the ring being horizontal. As the c) A is true but R is false.
switch is closed, the ring will move away from the solenoid. d) A is false but R is true.
38) Assertion (A): The induced e.m.f. and current will be same
in two identical loops of copper and aluminium, when rotated
with same speed in the same magnetic field.
Reason (R): Induced emf in the ring, ε = dΦ Reason (R): Induced e.m.f. is proportional to rate of change
of magnetic field while induced current depends on resistance
dt

a) Both A and R are true and R is the correct explanation

of wire.
of A.
b) Both A and R are true but R is not the correct expla- a) Both A and R are true and R is the correct explanation
nation of A. of A.
c) A is true but R is false. b) Both A and R are true but R is not the correct expla-
d) A is false but R is true. nation of A.
c) A is true but R is false.
35) Assertion (A): At any instant, if the current through an in-
d) A is false but R is true.
ductor is zero, then the induced emf may not be zero.
Reason (R): An inductor tends to keep the flux constant. 39) Assertion (A): Inductance coil are made of copper.
a) Both A and R are true and R is the correct explanation Reason (R): Induced current is more in wire having less
of A. resistance.
b) Both A and R are true but R is not the correct expla- a) Both A and R are true and R is the correct explanation
nation of A. of A.
c) A is true but R is false. b) Both A and R are true but R is not the correct expla-
d) A is false but R is true. nation of A.
36) Assertion (A): Only a change of magnetic flux with time, c) A is true but R is false.
will maintain an induced current in the coil. d) A is false but R is true.
Reason (R): The presence of a large magnetic flux will 40) Assertion (A): The figure shows a metallic conductor moving
maintain an induced current in the coil. in a magnetic field. The induced emf across its ends is zero.
a) Both A and R are true and R is the correct explanation
of A.
b) Both A and R are true but R is not the correct expla-
nation of A. Reason (R): The induced emf across the ends of a conductor
c) A is true but R is false. is given by e = Bvl sin θ .
d) A is false but R is true.
a) Both A and R are true and R is the correct explanation
37) Assertion (A): Magnetic flux can produce induced e.m.f.
of A.
Reason (R): Faraday established induced e.m.f. experimen-
b) Both A and R are true but R is not the correct expla-
tally.
nation of A.
a) Both A and R are true and R is the correct explanation c) A is true but R is false.
of A. d) A is false but R is true.