1. 10/09/2018
Electromagnets
Know that there is a magnetic field around a wire in which a current is flowing.
Investigate the how to change the strength of an electromagnet.
Know how to use electricity to make and destroy magnets.
Explain how electromagnets are used in some common devices.
Mr B. Smith

2. Electromagnets
Know that there is a magnetic field around a wire in which a current is flowing.
Know how to use electricity to make and destroy magnets.
Explain how electromagnets are used in some common devices.

3. Circuit Breakers Circuit breakers can be used instead of fuses.
They contain an electromagnetic switch, which trips, to break the circuit, if the current gets too high.
Circuit breakers respond faster than fuses and they can be easily reset.
Credit: ANDREW LAMBERT PHOTOGRAPHY / SCIENCE PHOTO LIBRARY CREDIT MUST BE GIVEN IN FULL Caption Domestic circuit breakers in a house. The circuit breakers (right) cut the electricity supply to a device when a fault develops. At left is the electricity meter. This records the amount of electricity used by the house, which is used for billing purposes. 3

4. Magnetism and Electric Currents
10 September 2018
Mr B. Smith
Magnetism and Electric Currents
An electric current flowing through a wire produces a magnetic field.
Copy the diagram
Current
MARTYN F. CHILLMAID / SCIENCE PHOTO LIBRARY CREDIT MUST BE GIVEN IN FULL Caption Magnetic field round an electric wire. Iron filings (grey) being used to show the circular magnetic field associated with an electrical wire. The wire (brown) is running vertically down towards the paper on which the filings have been scattered. Magnetism is caused by the regular alignment of electrons within materials like metals, which explains why a regular flow of electrons (an electric current) produces the same phenomenon. 4 4

5. 10 September 2018
Mr B. Smith
Electromagnets
An electric current flowing through a wire produces a magnetic field.
Electromagnets can be very strong.
They can be also switched on and off.
Credit: CORDELIA MOLLOY / SCIENCE PHOTO LIBRARY CREDIT MUST BE GIVEN IN FULL Caption Electromagnet on a crane being used to lift waste metal at a scrapyard. An electromagnet is only magnetised when an electric current is flowing through it, allowing it to be turned on and off when required. 5 5

6. 10 September 2018
Mr B. Smith
Solenoids
A coil of wire which has a current flowing through it is called a solenoid.
A core of iron can make an electromagnet stronger.
A solenoid’s magnetic field has the same shape as a bar magnet’s field.
Credit: ANDREW LAMBERT PHOTOGRAPHY / SCIENCE PHOTO LIBRARY CREDIT MUST BE GIVEN IN FULL Caption Magnetic field of a solenoid. Solenoid (centre) and iron filings (black) marking the field lines of its magnetic field. A solenoid is simply a coil of electrical wire. When electricity flows through the wire, a magnetic field is created. Any current flowing through a wire will have a magnetic field, but the coiling of a lot of wire produces a strong magnetic field like that of a bar magnet. This is a phenomenon known as electromagnetism, and the solenoid is known as an electromagnet. It can be used to magnetize materials like iron, and also to generate motion (as in an electric motor) and to generate electricity (as in a dynamo). 6 6

7. Practical: Making an Electromagnet
Aim: Investigate how changing the number of coils effects the strength of an electromagnet.
Use a low voltage so that the wire does not get too hot.
Make sure the coils are held at one end of the core.
Write down your aim, method (including diagram) and results table. 7

8. Practical: Making an Electromagnet
Aim: Investigate how changing the number of coils effects the strength of an electromagnet.
Use a low voltage so that the wire does not get too hot.
Make sure the coils are held at one end of the core.
Results
Number of Coils
Number of Paperclips 2 4 6 8 10 … 8

9. 10 September 2018
Mr B. Smith
Conclusions
Which electromagnet could pick up the most paperclips?
Which electromagnet was strongest, and why?
Three factors can be changed to make a strong electromagnet:
a larger current
more coils of wire
a core of iron 9

10. Making and Destroying Magnets Using Electricity
A coil carrying direct current (DC) will align all the domains in a magnetic material.
It will become a magnet.
A coil carrying an alternating current (AC) will jumble up (randomise) all the domains in a magnetic material.
It will be unmagnetised. S N

11. Magnetically Soft and Magnetically Hard Materials
A soft iron core in an electromagnet will lose its magnetism when the current is switched off.
If a core of steel is used it will remain magnetic even after the current has been switched off.
A material that remains magnetised is called magnetically hard.
A material that loses its magnetism quickly is called magnetically soft.

12. Fuses A fuse is connected to the live wire in a three-pin plug.
The fuse contains a thin wire.
If too much current flows through the fuse the wire will melt, breaking the circuit.
Credit: SHEILA TERRY / SCIENCE PHOTO LIBRARY CREDIT MUST BE GIVEN IN FULL Caption Three-pin plug. The inside of a three-pin plug and a selection of fuses. A fuse consists of a fine wire which protects an electrical appliance from overload. If the current rises too high the fuse melts and breaks the circuit. The live wire has brown insulation, neutral blue , earth green and yellow. Each wire is connected to the appropriate plug pin. The 3-pin plug is used in the U.K. to connect domestic appliances and tools to the national 240 volt alternating current supply. The earth wire is an electrical connection between the appliance and the ground. In the event of a fault in the appliance the current flows to earth causing no harm to the user. 13

13. Types of Fuses Cartridge Fuses These fit inside three-pin plugs
Fuse Wires
These fit inside a property’s fuse box
Credit: ANDREW LAMBERT PHOTOGRAPHY / SCIENCE PHOTO LIBRARY CREDIT MUST BE GIVEN IN FULL Caption Electrical fuses. 3A, 5A and 13A (A is short for ampere) fuses, designed to protect electrical devices and people from excessive currents. When the fuse is connected in an electrical circuit, an electrical load of more than the stated limit will melt the thin wire in the fuse, cutting off the electrical supply.
Credit: SHEILA TERRY / SCIENCE PHOTO LIBRARY CREDIT MUST BE GIVEN IN FULL Caption Fuse wires. Three different strengths of fuse wire wrapped around a cardboard holder. The different strengths are for use in different types of electrical circuit in the home. The strength of the wire depends upon it thickness. The weakest, and thinnest, is the five ampere (amp) fuse, with the thirty amp fuse being the strongest, and thickest. Fuse wire is a safety feature used to protect electrical circuits from excessive currents. At a specific current the fuse wire melts, or 'blows', breaking the circuit. 14

14. Reed Switches A reed switch is a type of relay.
10 September 2018
Mr B. Smith
Reed Switches
A reed switch is a type of relay.
A reed switch contains thin pieces of metal.
Putting a reed switch near a magnetic field will move the armature
This can be used to switch circuits on or off.
Credit: ANDREW LAMBERT PHOTOGRAPHY / SCIENCE PHOTO LIBRARY CREDIT MUST BE GIVEN IN FULL Caption Reed switch without coil. This is an electrical component that is placed in a circuit to allow the circuit to be switched on and off by completing or breaking the circuit. Inside the glass tube are two springy metal contacts that are normally not in contact (the circuit is said to be broken). The contacts are brought together (the switch is said to be turned on) either by an electromagnet or by a permanent magnet (not seen) that magnetizes the contacts. This causes them to attract each other and bend to make contact. When the magnetism is lost, the contacts spring apart. For a reed switch with its electromagnetic coil, see T355/243.
Title: Reed switch SPL Reference Number: T355/243 Uncompressed digital file size: 50 MB Downloadable digital file size: 3.6 MB Credit: ANDREW LAMBERT PHOTOGRAPHY / SCIENCE PHOTO LIBRARY CREDIT MUST BE GIVEN IN FULL Caption Reed switch with coil. The reed switch, inside the coil of wire, is an electrical component that is placed in a circuit to allow the circuit to be switched on and off by completing or breaking the circuit. The switch is activated by magnetism, here by an electromagnetic coil. The electricity that flows through the coil magnetizes whatever is inside it. In this case, it magnetizes two metal contacts inside the switch. These contacts attract each other, bend, and touch. This completes the circuit. When the electromagnet is switched off, the magnetism is lost, and the contacts spring apart. For internal details, see T355/242. 15 15

15. Speakers A speaker converts an electrical signal into sound waves.
Changing the current flowing in the coil of wire alters its magnetic field.
The coil, attached to the speaker’s diaphragm, moves as it is attracted to/repelled from the permanent magnet.
The movement of the diaphragm produces the sound waves.
Explain how a speaker works. Include a diagram in your answer.
Credit:  ANDREW LAMBERT PHOTOGRAPHY / SCIENCE PHOTO LIBRARY
Caption:  Dismantled loudspeaker. This is a device that is designed to convert electrical signals into sound waves. The two fixed components are the permanent magnet (black, lower centre) and a metal framework (the basket, grey). The magnet surrounds the voice coil (orange, centre). This is an electromagnetic coil that vibrates relative to the magnet when the electric sound signal is sent through it. The coil is held in place by the flexible spider structure (corrugated, red), but is also attached to the diaphragm (black). As the coil vibrates, it moves the diaphragm, producing the air pressure waves that are called sound waves.

16. Electric Guitar Pickup
How do an electric guitar’s pickups and amplifier allow us to hear?
Credit:  GUSTOIMAGES / SCIENCE PHOTO LIBRARY
Caption:  Guitar and amp, X-ray. An electric guitar, unlike an acoustic guitar, has no means of amplifying the sound made on its strings. An amplifier (amp) converts the signal sent electrically to it into sound. The circular structure (lower right) is a speaker and above this is a row of buttons, which control volume and various sound effects.

17. Homework