Question

Assertion : When the speed of an electron increases its specific charge decreases.

Reason: Specific charge is the ratio of the charge to mass.

• A. Both assertion and reason are true and the reason is the correct explanation of the assertion.
• B. Both assertion and reason are true but reason is not the correct explanation of the assertion.
• C. Assertion is true but reason is false.
• D. Assertion and reason both are false.
• E. Assertion is false but reason is true.

Answer 1

The correct option is B

Both assertion and reason are true but reason is not the correct explanation of the assertion.

Charge does not change with speed but mass varies with the speed as per relation $m=\frac{m_0}{\sqrt{1-\frac{v^2}{c^2}}}.$ Hence specific charge e/m decreases with increase in speed.