AQA GCSE Dynamos (Physics)
Dynamos
A dynamo uses the generator effect to generate a direct current, dc.
A direct current is one that travels in only one direction
Construction of a dynamo.
A dynamo has a similar construction to an alternator, but it has a split ring commutator, instead of slip rings.
How a dynamo works
As the coil turns in the magnetic field it will cut the magnetic field lines and induce a potential difference across the ends of the coil.If this is part of a complete circuit, then a current will flow.
However, the split ring commutator will swap the contacts every half turn. As a result, the induced potential difference will not reverse its direction like a alternator.
Instead the induced potential difference will vary from zero to a maximum value twice per cycle, in one direction or polarity only.
Increasing the peak value
The size of the peak value of the potential difference can be increased by:
1.The stronger the magnetic field in the dynamo, the greater the induced voltage.
2.More turns in the coil mean a higher induced voltage, since voltage is proportional to the total magnetic flux change through all loops.
3.The faster the coil spins within the magnetic field, the quicker the magnetic flux changes, which increases the peak induced voltage.
4.A larger coil area intercepts more magnetic flux, increasing the induced voltage.
5.Orientation of the Coil relative to the Magnetic Field. If the coil is arranged so it cuts the field lines, then a maximum induced voltage is produced across ends of the coil. If the coil is arranged, so the field lines are not cut, then the induced potential difference is 0V.
Practice Questions
1.A dynamo is used to produce a current that flows in one direction, or constantly changes direction?
2. Describe how the construction of dynamo is different to that of an alternator
3. Explain how a dynamo is used to produce an induced potential difference across the ends of the coil.
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