Question

Which of the following cannot be the shape of the path of a charged particle moving in a uniform magnetic field?

• A. straight line
• B. parabolic
• C. circular
• D. helical

Answer 1

The correct option is C circular

It will be a circular path with radius

$r=\left(\frac{mc}{qB}\right)$

and time period of

$T=(2\times pi\times \frac{m}{qB})$

This you can get from study of force on moving charge in magnetic field.

This is similar to cyclotron except that, in cyclotron, there is presence of electric field in addition to magnetic field. Hence in cyclotron, the radius of circular path keeps on increasing as speed of charge increases.