Video Lecture
Theory For Notes Making
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Ut elit tellus, luctus nec ullamcorper mattis, pulvinar dapibus leo.
Objective Assignment
Q.1
In the given figure a conducting rod is held between the poles of a permanent magnet. An electric potential difference will be induced between the ends of the conductor when it is moved in the direction of
(a) P (b) Q (c) L (d) M
Ans. (d)
Q.2
A wire frame ABCD and a current – carrying conductor xy lie in the same plane. Now of the frame is rotated about xy.
(a) No current will flow in ABCD
(b) Current will flow in the direction ABCDA
(c) Current will flow in the direction ADCBA
(d) The current will depend on distance x between xy and AB.
Ans. (a)
Q.3
Two identical co-axial circular loops carry a current i, each circulating in the same direction. If the loops approach each other then
(a) Current in each increases
(b) The current in each decreases
(c) The current in each remains same
(d) The current in 1 increases where as current in 2 decreases
Ans. (b)
Q.4
A conducting circular loop is placed inside a long solenoid carrying a current, such that the plane of loop is parallel to the axis of solenoid. If the current in the solenoid is varied, the induced current in the loop will be
(a) clockwise
(b) anticlockwise
(c) zero
(d) depends on the direction of current in solenoid
Ans. (c)
Q.5
In the figure, the key K is pressed to close the circuit of the solenoid X. Which of the following statements A to E is correct?
(a) a momentary currents flows in the solenoid Y circuit, from R to Q
(b) no current flows along QR
(c) the coil Y is attracted to X
(d) a momentary current flows from Q to R
Ans. (d)
Q.6
A solenoid in horizontal position, connected to a battery and a switch is placed on a table. A copper ring is placed at some distance apart with its axis coinciding with solenoid. and is at a distance. When current is allowed through by closing the switch. The ring will
(a) remain stationary
(b) move towards the solenoid
(c) move away from the solenoid
(d) will rotate about the axic
Ans. (a)
Q.7
The magnetic flux F(in weber) in a closed circuit of resistance 10 ohm varies with time t (in seconds) according to equation F = 6t2 – 5t + 1. The magnitude of induced current at
t = 0.25 s is
(a) 1.2 A (b) 0.8 A (c) 0.6 A (d) 0.2 A
Ans : (d)
Q.8
According to Faraday’s law of electromagnetic induction,
(a) an electric field is produced by time-varying magnetic flux
(b) a magnetic field is produced by time-varying electric flux
(c) a magnetic field is associated with a moving charge
(d) none of the above
Ans : (a)
Q.9
Lenz’s law is a consequence of the law of conservation of
(a) charge (b) mass (c) momentum (d) energy
Ans : (d)
Q.10
Faraday’s law of electromagnetic induction is related to the
(a) law of conservation of charge
(b) law of conservation of energy
(c) third law of motion
(d) law of conservation of angular momentum
Ans : (b)
Q.11
A coil area A = 0.5 m2 is situated in a uniform magnetic field B = 4 Wb/m2 and makes an angle of 60° with respect to the magnetic field as shown. The value of the magnetic flux through the area A would be equal to :
(a) 2 weber
(b) 1 weber
(c) 3 weber
(d) (3/2) weber
Ans. (b)
Q.12
A magnet is moving towards a coil along its axis and the emf induced in the coil is e. If the coil also starts moving towards the magnet with the same speed, the induced emf will be
(a) e/2 (b) e (c) 2e (d) 4e
Ans : (c)
Q.13
An electron moves on a straight line path XY as shown in figure. The abcd is a coil adjacent to the path of electron. What will be the direction of current if any induced in the coil?
(a) No current is induced
(b) abcd
(c) adcb
(d) The current will reverse direction as the electron goes past the coil.
Ans. (b)
Q.14
In the figure, the flux through the loop perpendicular to the plane of the coil and directed into the paper is varying according to the relation,
F = 6t2 + 7t + 1
where F is in milliweber and t is in seconds. The magnitude of the emf induced in the loop at t = 2 s and the direction of induced current through R are
(a) 39 mV; right to left
(b) 39 mV; left to right
(c) 31 mV; right to left
(d) 31 mV; left to right
Ans. (d)
Q.15
A rectangular coil is placed in a region having a uniform magnetic field B perpendicular to the plane of the coil. An emf will not be induced in the coil if the
(a) magnetic field is increased uniformly
(b) magnetic field is switched off
(c) coil is rotated about the axis XOX¢
(d) coil is rotated about an axis perpendicular to the plane of the coil and passing through its centre O.
Ans. (d)
Q.16
A copper ring having a cut such as not to form a complete loop is held horizontally and bar magnet is dropped through the ring with its length along the axis of the ring. The acceleration of the falling magnet is
(a) g
(b) less than g
(c) more than g
(d) depends on the relative size of the cut
Ans : (a)
Subjective Assignment
Q.1
State Lenz’s law.
Q.2
State Faraday’s law of electromagnetic induction.
Q.3
What is the dimensional formula of magnetic flux?
Q.4
Does change in magnetic flux induce e.m.f. or current?
Q.5
A vertical metallic pole falls down through the plane of magnetic meridian. Will any e.m.f. be induced between its
Q.6
A rectangular wire loop of sides 8 cm and 2 cm with a small cut is moving out of a region of uniform magnetic field of magnitude 0.3 T directed normal to the loop. What is the emf developed across the cut if the velocity of the loop is 1 cm s–1 in a direction normal
to the
(a) longer side,
Ans. \displaystyle 2.4\,\times \,{{10}^{{-4}}}\,V, lasting 2s
(b) shorter side of the loop? For how long does the induced voltage last in each case?
Ans. \displaystyle 2.4\,\times \,{{10}^{{-4}}}\,V,lasting 8s
Q.7
An artificial satellite with a metal surface is orbiting the earth around the equator : Will the earth’s magnetism induce some current in it?
Q.8
Show that the rate of change of magnetic flux has the same units as induced emf.
Q.9
A small piece of metal wire is dragged across the gap between the pole pieces of a magnet in 10s. The magnetic flux between the pole pieces is \displaystyle 8\,\times \,{{10}^{{-4}}} Wb. Find the magnitude of induced emf.
Q.10
State and explain Lenz’s law. Give one example to illustrate the law. How will you verify it experimentally? Does it obey the principle of energy conservation?
Q.11
A 10 ohm coil of mean area 500 cm2 and having 1000 turns is held perpendicular to a uniform field of 0.4 ´ 10-4 T. The coil is turned through 180o in (1/10) s. Calculate
(a) the change in flux
Ans. 4 mWb
(b) the average induced emf
Ans. 40 mV
(c) the average induced current and
Ans. 4 mA
(d) the total induced charge.
Ans. 400 mC
Q.13
Predict the directions of induced currents in metal rings 1 and 2 lying in the same plane where current I in the wire is increasing steadily.
Ans : clockwise in 1 and anticlockwise in 2
Q.14
Project the polarity of the capacitor in the situation described in the figure.
Ans : Upper plate is Positive and Lower Plate is negative
Q.15
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.
Ans : Clockwise
Q.16
Use Lenz’s law to determine the direction of induced current in the situations described by Fig.:
(a) A wire of irregular shape turning into a circular shape;
Ans. Along adcd
(b) A circular loop being deformed into a narrow straight wire.
Ans. Along a’ d’ c’ b’
Q.16
Predict the direction of induced current in the situations described by the following Figs. (a) to (f ).
Ans.
(a) Along qrpq
(b) Along prq, along yzx
(c) Along yzx
(d) Along zyx
(e) Along xry
(f) No induced current
