GCSE A* REVISION NOTES


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P3

 P3.1.1: X-Rays

 

 

 P3.1.2: Ultrasound

 

 P3.1.3&4: Lenses and the Eye

 

 P3.2.1 & 3: Centre of Mass and Hydraulics

 P3.2.2: Moments

 P3.2.4: Circular Motion

 P3.3.1: The Motor Effect

 

An electric motor is a coil of wire suspended in between two permanent magnets of opposite polarisation. A turning force is produced when a current is passed through the coil of wire perpendicular to the magnetic field which produces an upwards force on one side and a downwards force on the other. This causes the coil of wire to turn but after half a turn the forces will stay in the same direction so the coil will eventually come to a stop vertically between the magnets after fluctuating either side.  In order to counteract this a commutator is used which consists of a split contact of +/- on the end of the power supply and brushing contacts that rest on this from the coil of wire. After half a turn the direction of current also switches due to the commutator meaning that the forces switch direction leading to a continual rotational force being applied to the coil in the same direction. In order to increase this force you to increase the current/voltage in the coil, increase the number of turns on the coil, increase the area of the coil or increase the strength of the permanent magnetic field.  Include a diagram to further explain the layout of the electric motor and how the commutator works.

 

 P3.3.2: AC generators & Transformers

 

The ratio between turns and voltage change is the same


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