Question

Assertion : If an electron and proton enter a perpendicular magnetic field with equal momentum, then radius of curve for electron is more than that of proton.
Reason : Electron has less mass than proton.

• A. If both the assertion and reason are true and reason explains the assertion.
• B. If both the assertion and reason are true but reason does not explain the assertion.
• C. If assertion is true but reason is false.
• D. If assertion is false but reason is true.

Answer 1

Answer: (D)

When a charged particle enters in perpendicular magnetic field than radius of curved path is given by
$r=\frac{m v}{q B}=\frac{p}{q B}$
As momentum $p$ is constant
$ \therefore r \propto \frac{1}{q}$
As $e^-$ and proton have same charge
$\frac{r_{e}^{-}}{r_{p}^{+}}=\frac{q_{e}^{-}}{q_{e}^{+}}=1$
Assertion is false, but reason is true