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Question 1
This question is about the operation of microphone. |
a) | Explain the function of a microphone.
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b) | Explain with reference to the diagram above, how a moving-coil microphone works.
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c) | State one way in which the magnitude of the induced potential difference could be increased without changing the incident sound.
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Question 2
Microphones are used to convert sound waves into electrical signals. This question is about the operation of microphones. |
a) | When a sound wave is incident on the diaphragm, it causes a current to be induced in the coil. Explain why a current is induced in the coil when a sound wave is incident on the diaphragm.
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b) | The manufacturer makes microphones with different numbers of turns on the coil. The table below shows how the maximum induced current varies with the number of turns on the coil. Plot a graph of number of turns against maximum induced current. Model answer
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c) | A customer requires a minimum output current of 33 mA. Estimate the lowest number of turns on the coil that would produce an output current of 33 mA.
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Question 3
This question is about the operation of a moving coil loudspeaker. |
a) | Explain how the moving-coil loudspeaker converts an electrical signal into a sound wave.
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b) | A student replaces the alternating current electrical signal with a direct current. Explain why the student no longer hears the music output.
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c) | State two ways in which the force on the speaker cone could be increased.
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Question 4
This question is about the operation of moving-coil loudspeakers. |
a) | Which of the following would increase the force on the moving coil in a loudspeaker? A reduce the current in the coil B use a direct current in the coil C increase the number of turns on the coil D use a weaker magnet
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b) | Which of the following correctly describes the sound wave produced by the loudspeaker? A compressions (regions of spaced out particles) and rarefactions (regions of particles close together B oscillations of air molecules are perpendicular to the direction of travel of the wave C pressure variations caused by compressions and rarefactions in the air molecules D randomly vibrating air molecules
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c) | Put the statements in correct order to describe the operation of a moving-coil loudspeaker.
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Question 5
This question is about the construction of a simple loudspeaker. |
a) | At the instant shown in the diagram above, the left hand electrode is positive and the right hand electrode is negative. State the direction of the force acting on the aluminium foil.
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b) | The student connects the foil to a signal generator providing an alternating current at 40 Hz. Explain why the aluminium foil emits a low pitched humming noise when connected to the signal generator.
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c) | State two ways in which the force on the aluminium foil could be increased.
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