Question

If an electron of velocity is $2i+4j$ is subjected to magnetic field of $4k$, then, for the electron ,

• A. speed will change
• B. path will change
• C. velocity is Constant
• D. momentum is Constant

Answer 1

Answer: (B)

path will change

$F=q(\overrightarrow{V}\times \overrightarrow{B})$
$=e\left[\right(2i+4j)\times 4k]$
$=e[-8j+16i]$ (By cross-product rule)
So, it has non-zero force, so it velocity direction changes so, path changes, velocity changes, momentum changes but magnitude of velocity is constant, so, speed remains constant.