Practice questions
Chapter 10
Electromagnetism
1. a Magnetic flux density is measured in tesla, T. Define the tesla.
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b Here is an image of a loudspeaker. Briefly explain how it produces a sound.
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c The magnetic flux density in a loudspeaker is about 0.5 T.
Calculate the force per metre of wire when a current of 100 mA flows through the coil.
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d What have you assumed about the shape of the magnetic field?
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[Total: 10]
1(3)
2. a A wire carrying a current passes between the poles of two magnets placed on a top pan
balance.
The balance is zeroed when the current is turned off. The current is turned up and the
reading on the top pan balance is taken.
The following results are obtained:
Current / A Mass/g
0 0.00
0.5 0.10
0.9 0.18
1.4 0.29
2.1 0.43
2.6 0.53
3.1 0.63
3.9 0.80
Plot a suitable graph to find the value of the flux density between the magnets.
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c What precautions would you take to make the results accurate?
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[Total: 10]
3. An electron is accelerated through a potential difference of 100 V before it enters a
magnetic field of flux density 20 mT. The electron moves in a circular path in the field.
Calculate the radius of the path.
-31 -19
(mass of the electron = 9.1 x 10 kg, charge on the electron = 1.6 x 10 C)
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[Total: 5]
[Total for test paper: 25]
3(3)