Question

When cathode rays moving horizontally pass through an electric field directed vertically downward, the rays would be deflected ________ .

• A. downward
• B. upward
• C. backward
• D. none of the above

Answer 1

The correct option is B upward

The electric field is directed vertically downward i.e. the upper plate is positively charged and the lower plate is negatively charged . Because $\overrightarrow{E}$ points in a direction from positive to negative.

When a cathode ray particle i.e. negatively charged particle enters the electric field, it will be following a parabolic trajectory and would be directed towards the positive plate. Since the positive plate is upward directed. So cathode ray will be directed upwards.