Question

Following figure shows the path of an electron that passes through two regions containing uniform magnetic fields of magnitudes $B_1$ and $B_2$. Its path in each region is a half circle,choose the correct option

• A. $B_1$ is in to the page and it is stronger than $B_2$
• B. $B_1$ is in to the page and it is weaker than $B_2$
• C. $B_1$ is out of the page and it is weaker than $B_2$
• D. $B_1$ is out of the page and it is stronger than $B_2$

Answer 1

The correct option is A $B_1$ is in to the page and it is stronger than $B_2$

Equating centripetal force with magnetic force,

$\frac{m{v}^2}{r}=qvB$

$r=\frac{mv}{qB}$

Thus path having greater r will have lower magnetic field. Therefore field $B_1$ is stronger.

Considering the right hand thumb rule, the direction of the magnetic field for region of magnetic field $B_1$ is into the page and where for region $B_2$ is out of the page.