Question

The figure shows a uniform magnetic field $B$ confined to a cylindrical volume and is increasing at a constant rate. The instantaneous acceleration experienced by an electron placed at $\text{P}$ is

• A. $\text{zero}$
• B. $\text{towards right}$
• C. $\text{towards left}$
• D. $\text{upwards}$

Answer 1

The correct option is B $\text{towards right}$

The direction of the induced electric field is the same as the direction of induced emf or induced current at that point.

Consider an imaginary circular loop of radius $r$ as shown in the figure.


As the inward magnetic field is increasing, then according to Lenz's law, the current will flow counterclockwise in this imaginary loop.

Therefore, the induced electric field, $E_{ind}$ will be directed along the left-hand side of the point $\text{P}$.

Hence, electrons will experience a force, $F_e$ on the right-hand side of point $\text{P}$. Thus, the instantaneous acceleration experienced by an electron placed at $\text{P}$ will be towards the right.

Therefore, $\left(\text{B}\right)$ is the correct answer.

Why this question? This question gives you a basic idea of how to find the direction of an induced electric field.