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### Section 17.1Induced voltage and induced current

• Magnet moving near coil

• Conducting wire moving in magnetic field

© Manhattan Press (H.K.) Ltd.

17.1 Induced voltage and induced current(SB p. 142)

Magnet moving near coillight-beam

galvanometer

Expt. 17B

Electromagnetic inductionA. Induced current in a coil

coil

magnet

Go to

Quiz

Go to

Discussion 1

© Manhattan Press (H.K.) Ltd.

17.1 Induced voltage and induced current(SB p. 143)

Magnet moving near coilExpt. 17A

Electromagnetic induction(data-logging)A. Induced current in a coil

bar magnet

data-logging

interface

coil

current sensor

© Manhattan Press (H.K.) Ltd.

N

induced voltage

17.1 Induced voltage and induced current(SB p. 143)

Magnet moving near coilchange of magnetic field

induced current

electromagnetic induction

© Manhattan Press (H.K.) Ltd.

17.1 Induced voltage and induced current(SB p. 143)

Faraday\'s lawFaraday\'s law of electromagnetic induction

conductor

+change of magnetic field

induced voltage

strength of voltage

rate of change of magnetic field

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N

17.1 Induced voltage and induced current(SB p. 144)

Direction of induced current – Lenz\'s lawLenz\'s law

induced current flows in a directionopposes the change producing it

induced current

© Manhattan Press (H.K.) Ltd.

of the magnet

17.1 Induced voltage and induced current(SB p. 144)

Direction of induced current – Lenz\'s lawrepulsive force

N

© Manhattan Press (H.K.) Ltd.

of the magnet

17.1 Induced voltage and induced current(SB p. 144)

Direction of induced current – Lenz\'s lawattractive force

S

© Manhattan Press (H.K.) Ltd.

17.1 Induced voltage and induced current(SB p. 145)

Direction of induced current – Lenz\'s lawno force

at rest

no current

© Manhattan Press (H.K.) Ltd.

N

17.1 Induced voltage and induced current(SB p. 145)

Factors affecting the magnitude of induced voltagemagnitude of induced voltageby

(1) moving magnet faster

(2) using stronger magnet

(3)no. of turns of coil

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(b)

(c)

17.1 Induced voltage and induced current(SB p. 146)

Example 1:

An aluminium ring vertically above a bar magnet falls through it as shown. Draw the induced current in the ring when

(a) the ring is moving towards the magnet,

(b) the magnet is inside the ring, and

(c) the ring is moving away from the magnet.

Solution

© Manhattan Press (H.K.) Ltd.

17.1 Induced voltage and induced current(SB p. 146)

Conducting wire moving in magnetic fieldExpt. 17B

Electromagnetic inductionB. Induced current in a long wire

light-beamgalvanometer

long wire

slab-shapedmagnets on an iron yoke

© Manhattan Press (H.K.) Ltd.

17.1 Induced voltage and induced current(SB p. 147)

Conducting wire moving in magnetic fielddata-logging

interface

Expt. 17A

Electromagnetic induction(data-logging)B. Induced current in a long wire

longwire

current sensor

slab-shaped magnets on an iron yoke

© Manhattan Press (H.K.) Ltd.

field

current

17.1 Induced voltage and induced current(SB p. 148)

Fleming\'s right hand ruleFleming\'s right hand rule

© Manhattan Press (H.K.) Ltd.

current

field

17.1 Induced voltage and induced current(SB p. 148)

Fleming\'s right hand rule© Manhattan Press (H.K.) Ltd.

current

motion

17.1 Induced voltage and induced current(SB p. 148)

Fleming\'s right hand rule© Manhattan Press (H.K.) Ltd.

17.1 Induced voltage and induced current(SB p. 149)

Fleming\'s right hand ruleno current

CAL Workshop 1

Induced voltage in a conducting wire

Thinking 1

© Manhattan Press (H.K.) Ltd.

17.1 Induced voltage and induced current(SB p. 149)

Factors affecting the magnitude of induced voltage(1) move the wire faster

© Manhattan Press (H.K.) Ltd.

17.1 Induced voltage and induced current(SB p. 149)

Factors affecting the magnitude of induced voltage(2) use wire with more turns

© Manhattan Press (H.K.) Ltd.

17.1 Induced voltage and induced current(SB p. 149)

Factors affecting the magnitude of induced voltage(3) use stronger magnet

Go to

Activity 1

© Manhattan Press (H.K.) Ltd.

The induced current

flows in an

anticlockwise direction.

(b)

There is no

current flowing

through the coil.

(c)

The induced

current flows in a

clockwise direction.

17.1 Induced voltage and induced current(SB p. 150)

Example 2:

A conducting loop moves across a magnetic field as shown. Draw the direction of induced current in the loop (if any) in each case.

(b)

(a)

(c)

Solution

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17.1 Induced voltage and induced current(SB p. 151)

Class Practice 1:

1. In which direction does the induced current flow (if any) when the conductor or magnet is moved in the ways as shown? Note that the arrows in (c) and (d) show the movements of the magnets.

Mark the direction of the current (if any) in each of the following diagrams.

Answer

(a)

(b)

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17.1 Induced voltage and induced current(SB p. 151)

Class Practice 1: (Cont)

1.

(c)

Answer

(d)

(e)

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metal frame

17.1 Induced voltage and induced current(SB p. 152)

Class Practice 1: (Cont)

2. When a copper rod is moving along a metal frame, an induced current flows as shown.

(a) In which direction is the copper rod moving?

Answer

By Fleming\'s right hand rule, the copper rod is moving to the left.

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metal frame

17.1 Induced voltage and induced current(SB p. 152)

Class Practice 1: (Cont)

2.(b) Due to the induced current, the rod experiences a force inside the magnetic field. In which direction does this force act on the rod?

Answer

By Fleming\'s left hand rule or Lenz\'s law, the force on the rod acts to the right.

It opposes the motion of the rod.

© Manhattan Press (H.K.) Ltd.

© Manhattan Press (H.K.) Ltd.

17.1 Induced voltage and induced current(SB p. 140)

Quiz1.Which of the following statements about coal-burning power plants and nuclear power plants is incorrect?

Answer

A. Coal-burning power plants generate direct current (d.c.) but nuclear power plants generate alternating current (a.c.).

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17.1 Induced voltage and induced current(SB p. 140)

Quiz (Cont)

2.Which of the following cannot be achieved by a simple transformer (power adapter)?

Return to

Text

Answer

C. Convert 220 V d.c. to 12 V d.c.

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17.1 Induced voltage and induced current(SB p. 141)

Discussion 1:In 1831, Michael Faraday (1791 – 1867) discovered that a current could be produced by moving a conductor through a magnetic field. The conductor was connected in a closed circuit. His discovery turned electricity from a scientific curiosity into a powerful technology.

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17.1 Induced voltage and induced current(SB p. 141)

Discussion 1: (Cont)One day, the Prime Minister of England came to see the demonstration of electricity. After that, he asked Faraday what electricity was good for. Do you know how did Faraday reply? If you were Faraday, how would you reply? Discuss with your classmates.

Answer

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17.1 Induced voltage and induced current(SB p. 141)

Discussion 1: (Cont)After the Prime Minister of England asked what electricity was good for, Faraday replied that he did not have the answer yet, but he did know that one day the Prime Minister would put a tax on it.

Return to

Text

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17.1 Induced voltage and induced current(SB p. 149)

Thinking 1

In what situations does the electromagnetic induction happen?

Answer

1. Move a magnet near a conductor.

2. Move a conductor inside a magnetic field.

3. Change the magnitude of a magnetic field.

Return to

Text

© Manhattan Press (H.K.) Ltd.

17.1 Induced voltage and induced current(SB p. 150)

Activity 1 Fleming\'s right hand rule

Let\'s start:

1. Draw a card from the above pack of 6 cards to represent the direction of the magnetic field.

Into the paper

2. Then draw another card to represent the direction of the motion.

To left

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(into the paper)

motion

(to left)

current

17.1 Induced voltage and induced current(SB p. 150)

Activity 1 (Cont) Fleming\'s right hand rule

3. By Fleming\'s right hand rule, find the direction of the induced current.

4. Sketch a diagram to show the directions of the magnetic field, motion and induced current.

Into the paper

To left

Return to

Text

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