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ELECTROMAGNETISM (TRANSFORMERS (Ratio = primary:secondary (voltages and…
ELECTROMAGNETISM
MAGNETS
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MAGNETIC FIELD PATTERNS
When the north and south poles of two permanent magnets are placed close to each other, a uniform magnetic field is created.
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ELECTROMAGNETISM
In a flat, circular coil, the magnetic field in the centre is similar to a bar magnet. There are magnetic field line eclipses around the coil.
ELECTROMAGNETS
Solenoids are a a coil of wire wrapped around an iron core. Inside, the field is strong and uniform. Outside, the field is the same as a bar magnet.
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To increase the strength of a solenoid, increase the current or the number of turns of the coil or use a magnetically soft iron core.
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When there is current in a wire/conductor, a magnetic field is produced.
As current increases, the strength of the magnetic field increases.
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MAGNETIC MATERIALS
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An example would include iron. This is why it is used in transformers - so that it can be magnetised and demagnetised quickly.
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THE MOTOR EFFECT
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To experience the full force, the wire has to be at 90 degrees to the magnetic field. At angles in between, there is some force. When it is parallel, there is no force.
This causes a force on the wire. The force increases when the amount of current passing through the wire/conductor increases and when the strength of the magnetic field increases.
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LOUDSPEAKERS
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This causes a force on the cone outwards. When the direction of the current reverses, the cone moves inwards.
The vibration of the cone creates variations in air pressure, creating sound waves.
ELECTRIC MOTORS
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A split-ring commutator swaps the contacts every half turn to keep the motor rotating in the same direction.
The direction of the motor can be reversed can by swapping the polarity of the d.c. supply or swapping the poles.
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TRANSFORMERS
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When a.v. is in primary coil, the magnetically soft iron core magnetises and demagnetises quickly = induces a.v. in secondary coil.
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Efficiency in electricity transmission: Step-up to boost voltage (reduce loss of current), Step-down to reduce voltage = useful/safer to use.