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Magnetic fields (A-level only)

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Question 79

State Lenz's law.

A two-part diagram. The first part shows a top-down view of a single-turn square coil of side length 45 mm moving at a constant speed from Position 1, which is entirely outside a magnetic field, to Position 2, which is entirely inside. The magnetic field is uniform with a strength of 0.55 T and is directed vertically downwards into the page, represented by cross symbols. The coil is connected to an oscilloscope. The second part shows the same square coil entirely within the magnetic field, rotating about a horizontal axis of rotation represented by a dashed line through its center, also connected to the oscilloscope.

As shown in the diagram, a single-turn square coil of side length 45 mm45\text{ mm}45 mm is moved at a uniform speed from Position 1 to Position 2. While the coil is entering the uniform magnetic field of 0.55 T0.55\text{ T}0.55 T, the oscilloscope records an average induced electromotive force (emf) of 1.5 mV1.5\text{ mV}1.5 mV.

a.

Calculate the time, ttt, taken for the coil to move completely into the magnetic field from Position 1 to Position 2.

[4]
b.

The coil is now rotated at a constant angular speed about the horizontal axis of rotation shown in the diagram. Calculate the angular speed of the coil when the maximum reading on the oscilloscope is 9.2 mV9.2\text{ mV}9.2 mV.

[3]

Magnetic fields (A-level only) Questions

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