Question

If an electron describes half a revolution in a circle of radius r in a magnetic field B, the energy acquired by it is

• A. zero
• B. $\frac{1}{2}m{v}^2$
• C. $\frac{1}{4}m{v}^2$
• D. ${\mu }_r\times Bev$

Answer 1

The correct option is A zero

Since magnetic force is always perpendicular to the velocity of electron.

So it can only change the direction of velocity of electron.

But it (the magnetic force) cannot accelerate or deaccelerate the electron.