The following questions which appeared in Kerala Medical Entrance 2007 question paper are simple, as is usually the case as far as the questions on electromagnetic induction are concerned:
(1) A wire of length 50 cm moves with a velocity of 300 m/minute perpendicular to a magnetic field. If the emf induced in the wire is 2V, the magnitude of the magnetic field in tesla is
(a) 2 (b) 5 (c) 0.4 (d) 2.5 (e) 0.8
The emf (V) induced in a wire of length ‘L’ metre moving with velocity ‘v’ metre/second perpendicular to a magnetic field ‘B’ tesla is given by
V = BLv from which B = V/Lv
Be careful to convert the given velocity in to meter/second.
Thus we have B = 2/(0.5×5) = 0.8 tesla
(2) Whenever a magnet is moved either towards or away from a conducting coil, an emf is induced, the magnitude of which is independent of
(a) the strength of the magnetic field
(b) the speed with which the magnet is moved
(c) the number of turns in the coil
(d) the resistance of the coil
(e) the area of cross section of the coil
The magnetic flux linked with a circuit (and the emf induced) is independent of the resistance of the circuit. So the correct option is (d)
However, remember that the induced charge flowing in a circuit depends on the resistance as induced charge = (change of flux)/resistance
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