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igcse physics notesprinted 109 · PDF 109
124 pagesrevision 46936
printed 109 · PDF 109
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109
represents the direction of current, then the thumb represents the direction
of force. Fleming's left hand rule is applicable for motors.
What happens if we reverse directions?
If the current is revered, force is reversed
If the direction of magnetic field is reversed, force is revered
If both are reversed, the force remains the same.
A force is also exerted on charged particles moving in a magnetic field(
charged particles are current). If a beam of charged particles moves
through a magnetic field it will be deflected showing that there is force.
DC Motor working principle:
A DC motor consists of a coil of wire in between two permanent magnets.
Direct current flows through the wire and it experiences a turning effect due
to forces exerted on it in the magnetic field. As the current flows in opposite
directions on each side of the coil, the forces on each side are in opposite
directions making it turn. This turning effect can be increased by:
Increasing current
Increasing number of turns on coil of wire
Use a stronger magnet
A split ring commutator is used to ensure that the direction that current
flows in the coil reverses after every half rotation.