Question

What will be the directions of induced current when the loop enters the field and when it leaves the field?

Answer 1

Lenz’s Law and Induced Current Direction

According to **Lenz’s Law**, the direction of the induced current is such that it opposes the change in magnetic flux that produces it. Let’s examine this law in the context of a conducting loop entering and exiting a magnetic field directed into the plane of the paper (denoted by \( \times \) in the figure).

When the Loop Enters the Magnetic Field:

As the loop enters the region of the magnetic field, the magnetic flux through the loop increases because the area of the loop inside the magnetic field increases. To oppose this increase in flux, the induced current must create a magnetic field that opposes the original magnetic field.

Since the magnetic field is directed into the plane of the paper, the induced current must generate a magnetic field directed out of the plane of the paper (opposing the increase). Using the **right-hand rule**, this results in the induced current flowing in a **clockwise** direction.

When the Loop Leaves the Magnetic Field:

When the loop exits the magnetic field, the magnetic flux through the loop decreases because the area of the loop inside the field decreases. To oppose this decrease in flux, the induced current must generate a magnetic field that tries to maintain the original magnetic field directed into the plane of the paper.

To generate a magnetic field into the plane, the induced current must flow in an **anticlockwise** direction, again following the **right-hand rule** for the direction of the magnetic field created by the induced current.

Summary:

In summary, Lenz’s Law states that:

• When the loop enters the magnetic field, the induced current flows in a clockwise direction to oppose the increase in magnetic flux.
• When the loop leaves the magnetic field, the induced current flows in an anticlockwise direction to oppose the decrease in magnetic flux.