Electricity and Magnetism 7.2

Electric currents produce magnetic fields The iron filings show that the magnetic field of a current-carrying wire forms concentric circles around the wire.

Electricity and Magnetism – how are they related? When an electric current passes through a wire a magnetic field is formed. Direction of magnetic field reverses when current reverses Magnetic strength increases as the current increases.

Use the right-hand rule to find the direction of the magnetic field produced by a current If you imagine holding the wire in your right hand with your thumb pointing in the direction of the positive current, the direction your fingers would curl is in the direction of the magnetic field.

What is an electromagnet? When an electric current is passed through a coil of wire wrapped around a metal core, a very strong magnetic field is produced. This is called an electromagnet.

The magnetic field of a coil of wire resembles that of a bar magnet Increase strength of a magnetic field by adding more turns to a wire coil - solenoid, or increasing the current passing through wire. A solenoid has a north and south pole, like a magnet.

Electromagnetic Devices Galvanometers detect current . A galvanometer is an electromagnet that interacts with a permanent magnet. Stronger current = more interaction

What is a galvanometer? Galvanometers are used as gauges in cars and many other applications. The greater the current passing through the wires, the stronger the galvanometer interacts with the permanent magnet.

What are electric motors? An electric motor is a device which changes electrical energy into mechanical energy. In a simple electric motor, an electromagnet rotates between the poles of a permanent magnet.

How does an electric motor work?

Stereo speakers use magnetic force to produce sound Motion caused by magnetic force can even be used to produce sound waves.

What is electromagnetic induction? Moving a loop of wire through a magnetic field produces an electric current. This is electromagnetic induction. A generator is used to convert mechanical energy into electrical energy by electromagnetic induction.

Direct and Alternating Current

Direct and Alternating Current Direct Current (DC) - Current that flows in only one direction through a wire Ex: a battery

Alternating Current (AC) - Reverses the direction of the current flow in regular patterns Ex: a plugging a toaster into an outlet

Explain what happens when a magnet is placed near a current-carrying wire. A bar magnet is repelled when an electromagnet is brought close to it. Describe how the bar magnet would have moved if the current in the electromagnet had been reversed. Define the term electromagnetic force. Give an example of a machine that uses this force. Describe two ways that you could increase the strength of the magnetic field produced by an electromagnet. Explain how a simple electric motor transforms electrical energy into mechanical energy. How would an electromagnet's magnetic field change if the iron core were replaced by an aluminum core?

Explain what happens when a magnet is placed near a current-carrying wire. The magnet will be attracted to or repelled by the magnetic field of the current-carrying wire. If the wire or magnet is not held in place, they will move toward or away from each other. A bar magnet is repelled when an electromagnet is brought close to it. Describe how the bar magnet would have moved if the current in the electromagnet had been reversed. The bar magnet would have been attracted to the electromagnet. Define the term electromagnetic force. Give an example of a machine that uses this force. The electromagnetic force is the attractive or repulsive force between electric changes and magnets. Any machine containing a motor uses this force.

4. Describe two ways that you could increase the strength of the magnetic field produced by an electromagnet. increasing the current or the number of loops of wire 5. Explain how a simple electric motor transforms electrical energy into mechanical energy. The battery supplies electrical energy. The current in the coil creates an electromagnet. The electromagnet's poles are repelled and attracted by the permanent magnet's poles, causing the coil to spin. The spinning coil has mechanical energy. 6. How would an electromagnet's magnetic field change if the iron core were replaced by an aluminum core? The magnetic field would be weaker because aluminum is not a magnetic material.