# PHYS 2212 Module 7.5

## Force and Torque on a Current Loop

7.5 Force and Torque on a Current Loop

### Learning Objectives

By the end of this section, you will be able to:

• Evaluate the net force on a current loop in an external magnetic field
• Evaluate the net torque on a current loop in an external magnetic field
• Define the magnetic dipole moment of a current loop

### Magnetic Force on a Current-Carrying Loop

Continuing the discussion about the magnetic force on a current carrying wire, we will now look at what happens if we take a wire and bend it into a loop. We’re going to bend the wire into the shape of a rectangle because it makes the math easier. Then we will put that loop in a uniform magnetic field.

Using the RHR, determine the direction of the magnetic force on each side of the loop.

### Torque

Here is a quick reminder of how to calculate torque.

When a force (F) is applied to an object at some distance (r) away from a rotation point, then that object will rotate due to a torque. The torque is calculated with

where θ is the angle between r and F.

Practice!

See if you can use the RHR and your understanding of magnetic fields and forces to answer this:

### Magnetic Dipole Moment

Discuss!

The south pole of a bar magnet is brought toward the current loop.

Does the bar magnet attract the loop, repel the loop, or have no effect on the loop?