Question

A particle having a charge of $20\mu C$ and mass $20\mu g$ moves along a circle of radius 5 cm under the action of a magnetic field B=0.1 tesla. When the particle is at P, uniform transverse electric field is switched on and it is found that the particle continues along the tangent with a uniform velocity. Find the electric field :

• A. 2 V/m
• B. 0.5 V/m
• C. 5 V/m
• D. 1.5 V/m

Answer 1

The correct option is B 0.5 V/m

$r=\frac{mv}{Bq}$ (during circular path)
$\therefore v=\frac{Bqr}{m}$
Now $qE=Bqv$
$\therefore E=Bv=\frac{B^{2}qr}{m}$
$\therefore E=\frac{{\left(0.1\right)}^2(20\times {10}^{-6})(5\times {10}^{-2})}{(20\times {10}^{-9})}$
$=0.5V/m$