Magnetic Field Due to Straight Current Carrying Conductor
In the figure...
Question
In the figure, wires P1Q1 and P2Q2 are made to slide on the rails with same speed of 5 cms−1 . In this region, a magnetic field of 1 T exists in the direction as shown. The electric current in the 9 Ω resistor is
A
zero, if both wires slide towards left
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B
zero, if both wires slide in opposite directions
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C
0.2 mA, if both wires move towards left
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D
0.2 mA, if both wires move in opposite directions
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Solution
The correct option is C 0.2 mA, if both wires move towards left Each wire can be replaced by a battery whose emf is equal to Bℓv=1×4×10−2×5×10−2=20×10−4V
The polarity of the battery can be given by Fleming's right hand rule. When both wire move in opposite direction, the diagram looks like as shown in the figure.
The effective emf of the two batteries shown in the diagrams is zero.
So, choice (b) is correct and choice (d) is wrong.
When both wires move towards left, the circuit diagram looks
like as shown.
Effective emf of two batteries shown is E(=20×10−4V) and internal resistance is 1Ω . Hence, current in the circuit is i=20×10−410=0.2mA