1. Photograph 7.7(a) shows a straight wire in a circuit being
placed above a compass and parallel to the magnetic needle pointing north. When the circuit is closed, the magnetic needle is seen swinging to the right as shown in Photograph 7.7(b).
2. The deflection of the compass needle must be due to the presence of the magnetic field around the wire.
3. This shows that there is a relationship between the magnetic field and the current that flows through the wire.
4. The direction of the field lines can be determined by the right-hand grip rule.
If the right hand grips the wire so that the thumb points to the direction of current flow,
the wrapped fingers will point to the direction of the magnetic field.
The Meaning Of Electromagnetism And Electromagnet
1. The relationship between electricity and magnetism based on the fact that electric current can produce magnetic fields is known as electromagnetism.
2. When electric current flows through a coil of wire wrapped around a soft iron core, it creates a strong magnet called an electromagnet.
3. An electromagnet is a temporary magnet. When the current in the coil is switched on, the soft iron core becomes a magnet. If the current in the coil is switched off, the magnetism in the soft iron core disappears.
4. Soft iron is used because it can be magnetised and demagnetised easily.
5. Electromagnets are used in many appliances and machines. Doorbells, telephones and burglar alarms are some examples.
6. Powerful electromagnets are used in scrapyards to lift heavy pieces of metal.