In the diagram shown, the wires P1Q1 and P2Q2 are made to slide on the rails with the same speed of 5m/s. In this region, a magnetic field of 1T exists. The electric current in 9Ω resistor is
A
zero if both wires slide towards left
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B
zero if both wires slide in opposite direction
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C
20mA if both wires move towards left
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D
20mA if both wires move in opposite direction
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Solution
The correct option is C20mA if both wires move towards left The emf induced in each wire is given by
E=Bvl
E=1×5×0.04
E=0.2V
When both wires move in the opposite direction, the equivalent circuit can be drawn as
In this case, the net emf across 9Ω resistance is zero.
Hence, no current will flow through 9Ω resistor when wires move in opposite direction.
When both wires move towards the left, the equivalent circuit can be drawn as
Hence, current flowing through the 9Ω resistor is
i=0.29+1
i=0.210=0.02A
Or, i=20×10−3A=20mA
Hence, options (B) and (C) are the correct answers.