Question

At a place an electric field and a magnetic field are in downward direction. There an electron moves in downward direction. Hence this electron.

• A. Will bend towards left
• B. Will bend towards right
• C. Will gain velocity
• D. Will lose velocity

Answer 1

The correct option is D Will lose velocity

When a charge enters a region where bothelectric and magnetic field exists simultaneously, Lorentz force acts on it and is given by $\overrightarrow{F}=q[\overrightarrow{E}+(\overrightarrow{v}\times \overrightarrow{B}\left)\right]$

Since $\overrightarrow{v}$ and $\overrightarrow{B}$ are in same direction, $\overrightarrow{V}\times \overrightarrow{B}=vB\sin 0^0=0$ ,So, only electric force will act on it in upward direction $(\overrightarrow{F}=-q\overrightarrow{E})$ which is in opposite direction of the velocity.Hence this electron will lose velocity.

Therefore, D is correct option.