Electromagnetism: Answers

How can we determine the direction of a magnetic field in a wire which has a current running through it?

We can use the ‘right hand grip rule’ to determine the direction of a magnetic field in a current-carrying wire. If you grip the wire with your right hand, your thumb will be pointing in the same direction as the magnetic field.

What is a solenoid?

A solenoid is a coil of wire which can be used as an electromagnet.

Describe the magnetic field produced by a solenoid.

Solenoids have a strong, uniform magnetic field inside the coil. Outside the coil, the magnetic field is much weaker because the magnetic field lines have cancelled each other out.

How does an electric motor work?

An electric motor consists of a ring of wire surrounded on each side by two permanent magnets. The interaction of the magnetic field produced by the coil and the magnetic field produced by the permanent magnets created a force (the motor effect) which causes the ring of wire to turn. The electric motor contains a split-ring commutator which causes the direction of the current to increase, which enables the wire to experience a force on the opposite side. This ensures the motor keeps turning.

How can the speed of an electric motor be increased?

The speed of an electric motor can be increased by increasing the current, increasing the strength of the magnetic field or by increasing the number of turns on the coil.

Describe how loudspeakers make use of the motor effect to produce sound waves.

Loudspeakers consist of a coil of wire between two permanent magnets positioned at the base of a cone. The magnetic fields of the coiled wire and the permanent magnets interact, producing a force. This force causes the cone to move back and forth. These vibrations push the air molecules around the cone, creating sound waves.