Question

A charged particle is released from rest in a region of steady and uniform electric and magnetic fields which are parallel to each other. The particle will move in a ____________.

Options

• straight line

• circle

• helix

• cycloid

Answer 1

A charged particle is released from rest in a region of steady and uniform electric and magnetic fields which are parallel to each other. The particle will move in a straight line.

Explanation:

The particle is released from rest and `vec"E" || vec"B"`

`vec "F"_"E" = vec "F"_"E" + vec "F"_"B"`

`vec "F"_"E" = pm  "q"  vec"E" and vec "F"_"B" = pm  "q" (vec "v" xx vec "B")`

`"As"  vec"v" = 0, vec "F"_"B" = 0`

`"hence", vec "F"_"net" = vec "F"_"E"`

As `vec "F"_"E"` is acting along the direction of electric field, particle will always move in the direction of electric field. Also, `vec "v"` being parallel to `vec "B"`, particle will not deviate.