Electromagnetic Induction

Lenz's Law on electromagnetic induction is a direct result of the conservation of

• mass

• charge

• energy

• momentum

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If the number of turns in a circular coil is doubled but the current in the coil and the radius of the coil remain unchanged, which of the following statements best describes the change, if any, in the magnetic flux density produced by the coil?

• The magnetic flux density remains unchanged

• The magnetic flux density is doubled at all places

• The magnetic flux density is halved at all places

• The magnetic flux density increases at different rates for different points

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When a metal disc is rotated about its centre from a stationary state, with its plane perpendicular to a uniform magnetic field, an e.m.f. is induced between the centre of the disc and its edge. Which of the following statements, regarding the induced e.m.f. is true?

• The induced e.m.f. is zero when the angular velocity of the disc becomes constant

• The induced e.m.f. is directly proportional to the thickness of the disc

• The induced e.m.f. is proportional to the area of the disc

• The induced e.m.f. is inversely proportional to the resistivity of the disc material.

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The diagram below shows two identical wire coils X and Y both arranged along the same axis. P and Q can be moved along the axis of PQ running through the centre of each coil.

If coil Y carries a constant current I, then a current in the same direction as I will be induced in the coil X when

• coil X is moved away from coil Y

• coil Y is moved nearer to coil X

• both the two coils are moved closer to each other

• both the coils are moved with the same speed towards P

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___ Law says that the Induced current is proportional to the change of magnetic flux 

• Lenz'
• Faraday's
• Ampere's

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___ Law says that a current produced by an induced emf moves in a negative direction so that its magnetic field opposes the original change in flux

• Lenz'

• Faraday's

• Ampere's

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In 1831 who discovered electromagnetic induction?

• Thomas Edison
• Nikola Tesla
• Michael Faraday

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Faraday's law calculates voltage.

• True

• False

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Can you produce current in a wire with a magnet that is sitting still?

• Yes; having a magnet near a wire is enough to excite the electrons

• No; the magnetic field has to be changing to excite the electrons

• No; magnets cannot create electricity

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If a magnet is pushed into a coil, voltage is induced across the coil. If the same magnet is pushed

into a coil with twice the number of loops,

• one-half as much voltage is induced.

• the same voltage is induced.

• twice as much voltage is induced.

• four times as much voltage is induced.

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