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The coil is rotated - AQA - GCSE Physics - Question 9 - 2023 - Paper 2
Question 9
The coil is rotated. Explain why a direct current is induced in the coil. Sketch a graph on Figure 23 to show how the potential difference generated across the lam... show full transcript
Worked Solution & Example Answer:The coil is rotated - AQA - GCSE Physics - Question 9 - 2023 - Paper 2
Step 1
Explain why a direct current is induced in the coil.
Answer
When the coil rotates in the magnetic field, it cuts through magnetic field lines. This movement induces a potential difference across the coil. Since the coil is connected to a complete circuit, this induced potential difference results in a current flow. During each half-revolution, the configuration of the coil ensures that the ends connected to the brushes remain fixed in terms of direction. As a result, the current does not reverse direction every half rotation, allowing a direct current to be generated.
Step 2
Sketch a graph on Figure 23 to show how the potential difference generated across the lamp varies for two complete revolutions of the dynamo coil.
Answer
The graph for potential difference against time will exhibit a sinusoidal wave pattern. For two complete revolutions, the wave peaks will alternate, demonstrating periods of positive and negative potential differences. Each peak corresponds to the maximum induced potential when the coil is cut through the magnetic field lines maximally. A correct representation will show a negative output potential difference during the decreases.
Step 3
Explain why the dynamo becomes much easier to turn.
Answer
After the lamp is disconnected, there is no induced current flowing through the circuit. Consequently, this means that no magnetic field is produced around the coil. Without this opposing magnetic field, there is no force acting against the movement of the coil, making it significantly easier to turn the dynamo.