Question

A proton moving in a straight line enters a strong magnetic field along the field direction then its path and velocity will be

• A. path is circular but speed constant
• B. path is same but velocity increases
• C. path is same and velocity remains constant
• D. path is same and motion is retarded

Answer 1

The correct option is C path is same and velocity remains constant

$F=q(\overrightarrow{V}\times \overrightarrow{B})$
$=qVBsin0$
$=qVBsin{0}^0$ $(\because \text{V and B has same direction})$
$=0$ $(\because sin{0}^0=0)$
So, there is no force, so, path is same and velocity is constant.