1. Magnetism Magnets and electromagnets Catherine Mortimer-Hawkins, IEST

2. Magnets A magnet has 2 poles, a N-pole and a S-pole. The magneticfieldgoes from N to S.

3. Attraction or repulsion?

4. The earth’smagneticfield Ifwestand with loads of magnets on the surface of the earththeywould all pointtheir N poletowards the north! And theirS-pole towards the south. This is because the earth has a magnetic field. The earth’ssouthmagneticpole is near the earth’snorthgeographicpole!!

5. Magneticfield round a wire The danish scientist Hans Christian Örstednoticed that if you have a current in a wire therewill be a magneticfield. The thumbrule is: Imaginegrabbing the wire with your right hand. Thumb in the currents direction, your finger will thenpoint in the same direction as the fieldlines.

6. The magneticfield round a wire: The magneticfieldlines are circles. The field is strongestnearest the wire. Increasing the currentincreases the strength of the field.

7. Coils and solenoids A magneticfield round a wire will be strongerif it is woundinto a coil (spole). A longcoil is called a solenoid. The magneticfieldwillthen look like this:

8. The magneticfield of a coil: is increased by increasing the current. is increased by the number of turnsaround the coil. is reversedif the currentchangesdirection.

9. Thumbrule nr 2 Imaginegripping the coil with your right hand so that your fingers are in the same direction as the current. Your thumbwillthenpoint at the north of your electromagnet.

10. Different uses of a electromagnets: Relay Computer hard drive The curcuitbreaker A magnetic door lock Hugeelectromagnets on cranes Door bells