Assertion: The energy of charged particle moving in uniform magnetic field does not change.
Reason: Work done by magnetic field on the charge is zero.

Options

A. Both A and R are true and R is the correct explanation of A
B. Both A and R are true but R is NOT the correct explanation of A
C. A is true but R is false
D. A is false and R is true

Answer

A

Explanation

The force on a charged particle moving in a uniform magnetic field always acts in direction perpendicular to the direction of motion of the charge.
So work done by the magnetic field,
`W = FS cos theta = FS cos 90^(@) = 0`
So, the energy of the charged particle does not change.
Both, assertion and reason are true and reason also explains the assertion.