Consider the situation shown in Fig. The wire PQ has a negligible resistance and is made to slide on the three rails with a constant speed of `5 cm//s`.

Find the current in the `10 (Omega)` resistor when the switch S is thrown to
the middle rail

Options

A. zero
B. 2 mA
C. 3 mA
D. None of these

Answer

D

Explanation

Here `B=1T, v=5 xx 10^(-2) m//s, R=1 Omega`
When the switch is thrown to the middle rail `E=Bvl`
`=1 xx 5 xx 10^(-2) V`
`=10 xx 10^(-4) =10^(-3)V`
Current in the `10 Omega` resistor =`E//R`
`(10^(-3))/(10) =10^(-4) = 0.1 mA`
The switch is thrown to the lower rail
`E=Bvl`
`=1 xx 5 xx 10^(-2) xx 4 xx 10^(2) = 20 xx 10^(-4)V`
Current `=(20 xx 10^(-4))/(10) = 2 xx 10^(-4) = 0.2 mA`.