Question

A particle of mass m and charge $+Q$ is moving in a magnetic field of strength $B$. The particle moves in a circular path of radius $R$.
Which of the following changes would result in a circular path of radius $2R$?

• A. Double the mass
• B. Double the charge
• C. Reduce the speed by half
• D. Reduce the speed by four

Answer 1

The correct option is A Double the mass

Radius of the circular path $R=\frac{mv}{BQ}$

(A) : $m^{\prime }=2m$

$\therefore$ New radius $R^{\prime }=\frac{\left(2m\right)v}{BQ}=2R$

Hence option A is correct.