Question

A current-carrying wire in a magnetic field experiences a magnetic force: F=IL B sino (1) I is the current in the wire, L is the length of the wire in the B-field, B is the strength of the magnetic field, and q is the angle between the field and the wire. In this lab, a magnet is the source of the B-field that exerts a force on the wire. Because the wire is carrying current, it too creates a B-field that exerts a force on the magnet. In fact: Fupon wire = F (2) upon magnet

Part 1) If you double the current in the wire, what happens to the force on the wire? What about the force on the magnet?

Part 2) If you double the length of the wire, what happens to the force on the wire? What about the force on the magnet?

Part 3) If you double the magnetic field that the wire is in, what happens to the force on the wire? What about the force on the magnet?

Answer 1

Part 1)

From equation (1), Force on wire is directly proportional to current. When current is doubled, force on wire also doubles. By equation (2), force on magnet is equal to force on wire. Therefore force on magnet also doubles.

Part 2)

Force on wire is also directly proportional to length of the wire. So as length is doubled, the force acted on wire and force acting on magnet also doubles.

Part 3)

When magnetic field is doubled, since force is proportional to magnetic field, force on wire doubles and hence force on magnet also doubles.

To sum up in all three cases considered, force on wire and force on magnet doubles.