Question

An electron enters a magnetic field with a speed of ${10}^{8}cm/s$. The particle experiences a force due to the magnetic field and the speed of the electron

• A. will decrease
• B. will increase
• C. will remain constant
• D. may in crease or decrease

Answer 1

The correct option is C will remain constant

A particle travelling perpendicular to a magnetic field would experience a force given by $F=q(\overrightarrow{v}\times \overrightarrow{B})$.

This force, thus, acts perpendicular to the direction of motion of electron. Hence it only changes the direction of electron but not the speed of electron perpendicular to the direction of motion. This force would cause a constant centripetal acceleration. Thus the speed of electron does not change at all.