Question

A particle of charge $q$ and mass $m$ enters at speed $v$ into a uniform magnetic field of magnitude $B$.
If the particle is moving out of the page and the magnetic field is directed into the page as shown, which of the following correctly describes the path of the particle?

• A. In a circle that curves down the page.
• B. In a circle that curves up a page.
• C. In a clockwise circle in the plane of the page.
• D. In a counter-clockwise circle in the plane of the page.
• E. In a straight line out of the page.

Answer 1

The correct option is E In a straight line out of the page.

The force $F$ on a charge $q$ moving with velocity $v$ in a magnetic field $B$ is given by ,

$F=qvB\sin \theta$ ,

where $\theta =$ angle between v and B ,

in the given diagram the angle between v and B is , $\theta ={180}^o$ ,

therefore $F=qvB\sin 180=0$ ,

charge q doesn't experience any force so it will follow a straight line out of the page .