# 7.3.3 Graphs of Potential Difference in the Coil

Higher Tier Only

### Graphs of Potential Difference in the Coil

#### Oscilloscopes

• A device called an oscilloscope is used to show how the potential difference generated in the coil changes over time
• It will produce a line, called a trace, on a screen
• The vertical axis of the trace is the generated potential difference
• The higher the line, the greater the amount of potential difference induced
• The horizontal axis of the trace is time
• This allows the variation in potential difference against time to be shown

Trace of generated potential difference against time on an oscilloscope

#### Alternating Potential Difference Trace on an Oscilloscope

• An alternator consists of a rotating magnet next to (or inside) a coil

Alternating potential difference trace showing the position of the magnet relative to the coil

• When the magnet is in position 1 the magnetic field lines of the magnet do not cut the coil
• This means that there is no potential difference induced in the coil
• When the magnet is in position 2 the magnetic field lines of the magnet are at 90o to the coil
• This means that there will be maximum potential difference induced in the coil
• When the magnet is in position 3 the magnetic field lines of the magnet do not cut the coil
• This means that there is no potential difference induced in the coil
• When the magnet is in position 4 the magnetic field lines of the magnet are at 90o to the coil
• This means that there will be maximum potential difference induced in the coil
• As the poles of the magnet are reversed compared to position 2 the induced potential difference will also be in the opposite direction compared to position 2
• This means that the trace is negative

#### Direct Potential Difference Trace on an Oscilloscope

• A dynamo consists of a coil, which is rotated by a mechanical process, inside a magnetic field

Direct potential difference trace showing the position of the coil relative to the magnetic field

• When the coil is in position 1 the magnetic field lines of the magnet do not cut the coil
• This means that there is no potential difference induced in the coil
• When the coil  is in position 2 the magnetic field lines of the magnet are at 90o to the coil
• This means that there will be maximum potential difference induced in the coil
• When the coil is in position 3 the magnetic field lines of the magnet do not cut the coil
• This means that there is no potential difference induced in the coil
• When the coil is in position 4 the magnetic field lines of the magnet are at 90o to the coil
• This means that there will be maximum potential difference induced in the coil
• The trace will remain positive because there has been no change to the direction of the magnetic field

### Author: Katie

Katie has always been passionate about the sciences, and completed a degree in Astrophysics at Sheffield University. She decided that she wanted to inspire other young people, so moved to Bristol to complete a PGCE in Secondary Science. She particularly loves creating fun and absorbing materials to help students achieve their exam potential.
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