Is an electromagnet a temporary or a permanent magnet?
- A permanent magnet is a magnet that retains its magnetion. A small permanent magnet can be used to hold notes onto the door of a refrigerator. Neodymium magnets are very powerful permenent magnets used in hard drives of computers.
- Sometimes we do not want a magnet to stay magnetised all the time. We want it to lose its magnetism so that it can release the object attracted to it. Such magnets are called temporary magnets.
- An electromagnet is a temporary magnet. It is made by winding a coil of insulated wire round a soft iron core.
When a current is passed through the coil, the magnetic field produced by the current magnetises the soft iron core. The soft iron core loses all the magnetism when the current is switched off.
- An electromagnet is a temporary magnet which magnetic field is produced by the flow of electric current in a coil wound round a soft iron core.
The electromagnet uses the magnetic effect of an electric current. A wire carrying a current produces a magnetic field in the region around the wire.
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What are some devices that use electromagnets?
Applications of Electromagnets:
- heavy iron or steel objects such as scrap iron from place to place.
- The electromagnet is placed at the end of the cable at the arm of a crane.
- It consists of a circular soft iron core and windings made of insulated copper wire.
- There are opposite poles on the surface of the electromagnet as shown in Figure. This produces a stronger magnetic field to enable the electromagnet to lift heavier objects.
- When the power supply is switched on, the soft iron is magnetised to become a very powerful magnet.
- It lifts up iron and steel objects and separate them from non-magnetic objects.
- When the crane has moved to a new location, the power supply is switched off and the objects fall off.
- The electric bell is commonly used in schools as the fire alarm systems.
- The electric bell has a very simple but efficient design. There are very few moving parts. A well made electric bell can last for many years.
- An electromagnetic relay connects a primary circuit to a secondary circuit.
- A small current in the primary circuit will switch on a larger current in the secondary circuit.
- A relay is used in the starter system of a car. When the driver turns the key to start the engine, a small current is switched on in the primary circuit.
- Figure explains how the relay switches on a larger current in the secondary circuit to operate the starter motor of the car.
- A circuit breaker acts as an automatic switch that breaks open a circuit and switches off the current when the current becomes too large.
- In a household circuit, the current may become excessive when there is a short-circuit or an overload.
- When the current increases, the strength of the magnetic field of the electromagnet increases suddenly. The soft iron armature is pulled towards the electromagnet, as shown in Figure.
- This results in the spring pulling apart the contacts. The circuit is broken and the current flow stops immediately.
After repairs have been made, the reset button is pushed to switch on the current again.
- The permanent magnet attracts the magnetic alloy diaphragm with a constant force.
- When the caller at the other end of the line talks into the microphone, the earpiece receives a changing current from the telephone line.
- The changing current in the coils of the electromagnet changes the strength of the magnetic field. Therefore, the magnitude of the attractive force on the diagram also changes.
- This causes the diaphragm to vibrate and reproduce the sound wave from the caller.