Question

A particle with charge q moves with a velocity v in a direction perpendicular to the directions of uniform electric and magnetic fields, E and B respectively, which are mutually perpendicular to each other. Which one of the following gives the condition for which the particle moves undeflected in its original trajectory?

Options

• `"v" = "E"/"B"`

• `"v" = "B"/"E"`

• `"v" = sqrt("E"/"B")`

• `"v" ="q" "B"/"E"`

Answer 1

`"v" = "E"/"B"`

Explanation: 

When particle moves undeflected, magnetic force and electric force on particle exactly balance each other, i.e., `"F"_"m" = "F"_"e"`

qvB = qE `=> "v" ="E"/"B"`