A bar magnet is dropped vertically downwards through a long solenoid, which is connected to an oscilloscope. The oscilloscope trace shows how the e.m.f. induced in the coil varies with time as the magnet accelerates downwards. a A bar magnet falls through a long solenoid. b The oscilloscope trace shows how the induced e.m.f. varies with time. Explain why an e.m.f. is induced in the coil as the magnet enters it (section AB of the trace).

As the magnet (enters) spins, the magnetic field around the top and bottom of the coil constantly changes between a north and a south pole. There is a sudden increase in the flux linkage for the coil, This rotational movement of the magnetic field results in an alternating e . m . f . Being induced into the coil as defined by Faraday's law of electromagnetic induction.

A bar magnet is dropped vertically downwards through a long solenoid, which is connected to an oscilloscope . The oscilloscope trace shows how the e.m.f. induced in the coil varies with time as the magnet accelerates downwards. a A bar magnet falls through a long solenoid. b The oscilloscope trace shows how the induced e.m.f. varies with time. Explain why no e . m . f . is induced while the magnet is entirely inside the coil (section BC).

When, the magnet is entirely inside the coil there is no change in the flux linking of the coil. Although the stationary magnet might produce a large magnetic field, no e . m . f Can be induced because the flux through the coil is not changing. By Faraday’s and Lenz’s Law:- Faraday’s experiments showed that the e . m . f Induced by a change in magnetic flux depends on only a few factors. First, emf is directly proportional to the change in flux ΔΦ . Second, e . m . f Is greatest when the change in time Δt Is smallest—that is, emf is inversely proportional to Δt . Finally, if a coil has N Turns, an e . m . f Will be produced that is N Times greater than for a single coil, so that e . m . f Is directly proportional to N . The equation for the e . m . f Induced by a change in magnetic flux is e . m . f = - N ∆ Φ ∆ t Therefore, when no change in the flux linking of the coil there is no e . m . f is induced in the coil.

A bar magnet is dropped vertically downwards through a long solenoid, which is connected to an oscilloscope. The oscilloscope trace shows how the e.m.f. induced in the coil varies with time as the magnet accelerates downwards. a A bar magnet falls through a long solenoid. b The oscilloscope trace shows how the induced e.m.f. varies with time. Explain why section C D shows a negative trace, why the peak e , m , f , is greater over this section, and why C D represents a shorter time interval than AB.

Magnet leaves coil, there is a decrease in the flux linking the coil and hence the e . m . f . is in the reverse (negative) direction. The induced current is in the opposite direction (Lenz’s law). Peak e . m . f . is greater because the magnet is moving faster (acceleration due to gravity); the rate of change of flux linkage is greater.

E M B I B E

Physics for Cambridge International AS & A Level Coursebook 3rd Edition Digital Access>Chapter 26 - Electromagnetic Induction>Questions

David Sang and Graham Jones Solutions for Chapter: Electromagnetic Induction, Exercise 7: Questions

Author:David Sang & Graham Jones

David Sang Physics Solutions for Exercise - David Sang and Graham Jones Solutions for Chapter: Electromagnetic Induction, Exercise 7: Questions

Attempt the practice questions on Chapter 26: Electromagnetic Induction, Exercise 7: Questions with hints and solutions to strengthen your understanding. Physics for Cambridge International AS & A Level Coursebook 3rd Edition Digital Access solutions are prepared by Experienced Embibe Experts.

Questions from David Sang and Graham Jones Solutions for Chapter: Electromagnetic Induction, Exercise 7: Questions with Hints & Solutions

EASY

AS and A Level

IMPORTANT

Physics for Cambridge International AS & A Level Coursebook 3rd Edition Digital Access>Chapter 26 - Electromagnetic Induction>Questions>Q 15

A bar magnet is dropped vertically downwards through a long solenoid, which is connected to an oscilloscope. The oscilloscope trace shows how the e.m.f. induced in the coil varies with time as the magnet accelerates downwards.

Question Image

$a$ A bar magnet falls through a long solenoid. $b$ The oscilloscope trace shows how the induced e.m.f. varies with time.

Explain why an e.m.f. is induced in the coil as the magnet enters it (section AB of the trace).

EASY

AS and A Level

IMPORTANT

Physics for Cambridge International AS & A Level Coursebook 3rd Edition Digital Access>Chapter 26 - Electromagnetic Induction>Questions>Q 15

A bar magnet is dropped vertically downwards through a long solenoid, which is connected to an oscilloscope . The oscilloscope trace shows how the e.m.f. induced in the coil varies with time as the magnet accelerates downwards.

Question Image

$a$ A bar magnet falls through a long solenoid. $b$ The oscilloscope trace shows how the induced e.m.f. varies with time.

Explain why no $e . m . f .$ is induced while the magnet is entirely inside the coil (section BC).

EASY

AS and A Level

IMPORTANT

Physics for Cambridge International AS & A Level Coursebook 3rd Edition Digital Access>Chapter 26 - Electromagnetic Induction>Questions>Q 15

A bar magnet is dropped vertically downwards through a long solenoid, which is connected to an oscilloscope. The oscilloscope trace shows how the e.m.f. induced in the coil varies with time as the magnet accelerates downwards.

Question Image

$a$ A bar magnet falls through a long solenoid. $b$ The oscilloscope trace shows how the induced e.m.f. varies with time.

Explain why section $C D$ shows a negative trace, why the peak $e, m, f,$ is greater over this section, and why $C D$ represents a shorter time interval than AB.

EASY

AS and A Level

IMPORTANT

Physics for Cambridge International AS & A Level Coursebook 3rd Edition Digital Access>Chapter 26 - Electromagnetic Induction>Questions>Q 16

You can turn a bicycle dynamo by hand and cause the lamps to light up. Use the idea of Lenz's law to explain why it is easier to turn the dynamo when the lamps are switched off than when they are on.

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