Question

A positive charge enters with a velocity $v$ to the right, into a magnetic field coming out of the screen toward you.
The strength of the magnetic field is then doubled, how does this affect the motion of the charge through its circular path?

• A. The radius will increase.
• B. The tangential velocity will increase.
• C. The radius will decrease.
• D. The tangential velocity will decrease.

Answer 1

The correct option is C The radius will decrease.

Radius of the circular path traced $r=\frac{mv}{Bq}$

Now the strength of magnetic field is increased $B^{\prime }=2B$

$\therefore$ Radius of new circular path $r^{\prime }=\frac{mv}{\left(2B\right)q}=\frac{r}{2}$

Hence radius of circular path decreases.