Question

When electron beam passes through an electric field, they gain kinetic energy. If the same beam passes through magnetic field, then.

• A. Their energy increases
• B. Their momentum increases
• C. Their potential energy increases
• D. Energy and momentum both remains unchanged

Answer 1

Answer: (D)

Energy and momentum both remains unchanged

Answer 2

Because magnetic force always points

perpendicular to the particle velocity. That is why velocity remains unchanged thereby keeping energy $\left( \frac{1}{2}mv^{2} \right)$ and momentum (mv) unchanged.