Q.

A conducting rod of length  l  is moved at constant velocity v0 on two parallel conducting, smooth, fixed rails, that are placed in a uniform constant magnetic field B perpendicular to the plane of the rails as shown in figure. A resistance R is connected between the two ends of the rail. Then which of the following is/are correct

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a

Lenz’s law is not satisfied for direction of current in Loop

b

If resistance R is doubled then power required to maintain the constant velocity v0 becomes half

c

If applied external force is doubled then a part of external power increases the velocity of rod

d

The thermal power dissipated in the resistor is equal to rate of work done by external person pulling the rod

answer is A, B, D.

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Detailed Solution

Rate of workdone by external agent is dwdt=BiLdxdt=BilV and thermal power dissipated in the resistor = (BVl)I clearly both are equal.

If applied external force is doubled the rod will experience a net force and hence acceleration as a result velocity increasesI=eR on doubting ‘R’ current and hence required power becomes half P = BilV

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