MOTIONAL EMF
Figure shows a rectangular conductor PQRS in which the conductor PQ is free to move. The road PQ is moved towards the left with a constant velocity ‘v’ as shown in figure. Assume that there is no loss of energy due to friction. PQRS forms a closed circuit enclosing an area that changes as PQ moves. It is placed in a uniform magnetic field B which is perpendicular to the plane of this system. If the length RQ = x and RS = l, the magnetic flux φB enclosed by the loop PQRS will be
φB = Blx
Since x is changing with time, the rate of change of flux will induce an emf in the conductor.
1. Find the correct statement from the following.
i. Motional emf is inversely proportional to the speed of the conductor
ii. Motional emf is inversely proportional to the length of the conductor
iii. Motional emf is directly proportional to the magnetic field
iv. Motional emf is inversely proportional to the magnetic field
2. When the magnetic field is parallel to a surface, then the magnetic flux through the surface is:
i. Infinite
ii. Zero
iii. small but not zero
iv. large but not infinite
3. A wire of length 0.1 m moves with a speed of 10 m/s perpendicular to a magnetic field of induction 1 Wb/m2 . The emf induced will be
i. 10 V
ii. 0.01 V
iii. 0.1 V
iv. 1 V
4. A train is running on metre gauge at a speed of 36 km/hr. If the vertical component of the earth’s magnetic field is 4 x 10-5 T, then the emf generated between the railway lines will be
i. 4 V
ii. 4 mV
iii. 4 x 10-4 V
iv. 144 V
5. Identify the correct statements from the following:
The magnetic flux linked with a loop does not change with time when
a) Magnet and loop are moving with the same velocity in the same direction,
b) Magnet is rotated around its axis without changing its distance from the loop
c) Loop is moved in a uniform magnetic field and the whole of the loop remains in the field.
i. (a) and (c)
ii. (a) and (b)
iii. All the three statements correct
iv. (b) and (c)
