Graphs of Potential Difference in the Coil (AQA GCSE Physics)
Revision Note
Graphs of Potential Difference in the Coil
Potential difference graph for an alternator
The output of an alternator can be seen on a graph of potential difference (p.d.) against time, or angle of rotation
The shape of the graph is a sine or cosine curve, depending on the starting position of the coil
When it starts from a horizontal position (p.d. is at a maximum), the graph is a cosine curve
When it starts from a vertical position (p.d. is zero), the graph is a sine curve
Graph of induced p.d. with angle for an alternator
Alternating p.d. with corresponding positions of the coil relative to the field
When the coil is vertical at 0°
it is moving parallel to the direction of the magnetic field
the size of the induced p.d. is zero
When the coil has rotated by 90°
it is now horizontal and moving perpendicular to the direction of the magnetic field
the size of the induced p.d. is at a maximum
When the coil has rotated by 180°
it is vertical again and moving parallel to the direction of the magnetic field
the size of the induced p.d. is zero
When the coil has rotated by 270°
it is horizontal again and moving perpendicular to the direction of the magnetic field
the size of the induced p.d. is at a maximum and in the opposite direction to its position at 90°
When the coil has completed a full 360° rotation
it is back at its starting point where it is moving parallel to the direction of the magnetic field
the size of the induced p.d. is zero
Potential difference graph for a dynamo
The output of a dynamo can be seen on a graph of potential difference (p.d.) against time, or angle of rotation
The shape of the graph is a sine curve and is always in the same direction
Graph of p.d. with time for a dynamo
Direct potential difference trace showing the position of the coil relative to the magnetic field
When the coil is vertical at 0° (position 1)
it is moving parallel to the direction of the magnetic field
the size of the induced p.d. is zero
When the coil has rotated by 90° (position 2)
it is now horizontal and moving perpendicular to the direction of the magnetic field
the size of the induced p.d. is at a maximum
When the coil has rotated by 180° (position 3)
it is vertical again and moving parallel to the direction of the magnetic field
the size of the induced p.d. is zero
When the coil has rotated by 270° (position 4)
it is horizontal again and moving perpendicular to the direction of the magnetic field
the size of the induced p.d. is at a maximum and in the same direction as its position at 90° (i.e. position 2)
When the coil has completed a full 360° rotation (back to position 1)
it is back at its starting point where it is moving parallel to the direction of the magnetic field
the size of the induced p.d. is zero
Factors affecting alternator or dynamo output
The magnitude of the induced p.d. can be increased by:
increasing the frequency of rotation of the coil
increasing the number of turns on the coil
increasing the strength of the magnet
inserting a soft iron core into the coil
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