Question

A uniform electric field and a uniform magnetic field exist in a region in the same direction. An electron is projected with velocity pointed in the same direction the electron will

• A. turn to its right
• B. turn to its left
• C. keep moving in the same direction but its speed will increase
• D. keep moving in the same dirction but its speed will decrease

Answer 1

Answer: (D)

keep moving in the same dirction but its speed will decrease

Force due to magnetic field
$=q(\overrightarrow{V}\times \overrightarrow{B})$
$=qVBsin0$ $(\because sin{0}^0=0)$
$=0$ as velocity and field has same direction.
Force due to electric field
$=q\overrightarrow{E}$
So, electron has negative charge so force direction will be opposite to electric field direction.
So, electron will be moving in same direction but it's speed decreases.