Figure shows a conducting rod of negligible resistance that can slide on smooth U-shaped rail made of wire of resistance `1Omega//m`. Position of the conducting rod at `t=0` is shown. A time dependent magnetic field `B=2t` tesla is switched on at `t=0`
The magnitude of the force required to move the conducting rod at constant speed 5cm/s at the same instant `t=2s`, is equal to

Options

A. `0.16N`
B. `0.12N`
C. `0.08N`
D. `0.06N`

Answer

C

Explanation

`(C )` At `t=2s`, length of the wire `=(2xx30cm)+20cm =0.8m`
Resistance of the wire `=0.8 Omega`
Current through the rod `=(0.08)/(0.8)=(1)/(10)A`
Force on the wire `=i//B`
`=(1)/(10)xx(0.2)xx4=0.08N`
Same force is applied on the rod in opposite direction to make net force zero.