Electromagnetic Induction - Online Test

Q1. Use Lenz’s law to determine the direction of induced current in the situations described by the Figure (a) A wire of irregular shape turning into a circular shape; (b) A circular loop being deformed into a narrow straight wire. The directions for (a) and (b) respectively are

Answer : Option C
Explaination / Solution:

(a) for a given Periphery the area of a circle is maximum. When a coil takes a circular shape, the magnetic flux linked with the coil increases, so the current induced in the coil will tend to decrease the flux and so it will produce a magnetic field upward. As a result the current induced in the coil will flow in anticlockwise direction. (b) When circular coil takes the shape of narrow straight wire, The magnetic flux linked with the coil decreases. So the current induced in the coil will tend to oppose the decrease in magnetic flux. Hence it will produce an upward magnetic field so that the current induced in the coil will flow in anticlockwise direction.

Q2. 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  in a direction normal to the longer side. For how long does the induced voltage last?
Answer : Option A
Explaination / Solution:


duration of |e| is 


Q3. 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  in a direction normal to the shorter side of the loop? For how long does the induced voltage last ?
Answer : Option A
Explaination / Solution:


duration of |e| is 


Q4. A 1.0 m long metallic rod is rotated with an angular frequency of 400 rad  about an axis normal to the rod passing through its one end. The other end of the rod is in contact with a circular metallic ring. A constant and uniform magnetic field of 0.5 T parallel to the axis exists everywhere. Emf developed between the centre and the ring is
Answer : Option D
Explaination / Solution:

e=12Bωl2=12×0.5×200×1×1=100V
Q5.

A circular coil of radius 8.0 cm and 20 turns is rotated about its vertical diameter with an angular speed of 50 rad  in a uniform horizontal magnetic field of magnitude  T. If the coil resistance is , maximum emf induced in the coil,maximum value of current in the coil and average power loss due to Joule heating are


Answer : Option C
Explaination / Solution:



average power loss due to joule heating 


Q6.

A horizontal straight wire 10 m long extending from east to west is falling with a speed of 5.0 m , at right angles to the horizontal component of the earth’s magnetic field,  Wb m-2. Instantaneous value of the emf induced in the wire,direction of the emf and end of the wire which is at the higher electrical potential are


Answer : Option B
Explaination / Solution:


according to lenz's law direction of emf is  West to East


Q7. Current in a circuit falls from 5.0 A to 0.0 A in 0.1 s. If an average emf of 200 V induced, estimate of the self-inductance of the circuit is
Answer : Option D
Explaination / Solution:

L=edi/dt=2005/0.1=4H
Q8. A pair of adjacent coils has a mutual inductance of 1.5 H. If the current in one coil changes from 0 to 20 A in 0.5 s, change of flux linkage with the other coil is
Answer : Option A
Explaination / Solution:

Δϕ=MΔi=1.5×20=30Wb
Q9.

A jet plane is travelling towards west at a speed of 1800 km/h. If the Earth’s magnetic field at the location has a magnitude of  and the dip angle is , voltage difference developed between the ends of the wing having a span of 25 m is approximately


Answer : Option D
Explaination / Solution:


V = Vertical component of magnetic field


Q10.

It is desired to measure the magnitude of field between the poles of a powerful loud speaker magnet. A small flat search coil of area 2  with 25 closely wound turns, is positioned normal to the field direction, and then quickly snatched out of the field region. Equivalently, one can give it a quick  turn to bring its plane parallel to the field direction). The total charge flown in the coil (measured by a ballistic galvanometer connected to coil) is 7.5 mC. The combined resistance of the coil and the galvanometer is  . Field strength of magnet is


Answer : Option D
Explaination / Solution: