Section 16.1 Magnetic Force And Magnetic Field

Section 16.1 Magnetic force and magnetic field • Permanent magnet • Magnetic force • Magnetic field © Manhattan Press (H.K.) Ltd.

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16.1 Magnetic force and magnetic field (SB p. 105)

Permanent magnet Chinese discovered "lodestone" always points in N-S magnet

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Quiz

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Discussion 1

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16.1 Magnetic force and magnetic field (SB p. 106)

Permanent magnet et n g a m y r Eve has north th u o s & e l po pole

North points to Arctic © Manhattan Press (H.K.) Ltd.

South

N

S

points to Antarctic

Thinking 1 3

16.1 Magnetic force and magnetic field (SB p. 106)

Magnetic force

repel

S

N S

SN

N

N

N

S

NS

S

Like poles repel © Manhattan Press (H.K.) Ltd.

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16.1 Magnetic force and magnetic field (SB p. 106)

Magnetic force

attrac t

S

N S

SN

N

S

S

N

SN

N

Unlike poles attract © Manhattan Press (H.K.) Ltd.

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16.1 Magnetic force and magnetic field (SB p. 106)

Magnetic force Arctic

Arctic

Antarctic

N-poles point to Arctic

Antarctic

The earth is like magnet

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Activity 1

Thinking 2

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16.1 Magnetic force and magnetic field (SB p. 107)

Magnetic force compass — indicates direction accurately

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16.1 Magnetic force and magnetic field (SB p. 107)

Magnetic force magnets attract

paper clips

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16.1 Magnetic force and magnetic field (SB p. 108)

Magnetic force

S

N iron rod

Iron objects magnetized © Manhattan Press (H.K.) Ltd.

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16.1 Magnetic force and magnetic field (SB p. 108)

Magnetic force iron gold

N

silver copper

Thinking 3 © Manhattan Press (H.K.) Ltd.

aluminium

     10

16.1 Magnetic force and magnetic field (SB p. 108)

Class Practice 1: There are three metals X, Y and Z. From the following, determine which one is a magnet, a piece of iron, or a piece of aluminium. (i) X is attracted by a magnet no matter which pole of the magnet is facing it. (ii) Y is attracted or repelled by a magnet depending on the pole of the magnet. (iii) A magnet cannot attract or repel Z at all. Ans a piece of iron X is _______________________________. wer a magnet Y is _______________________________. a piece of aluminium Z is _______________________________. © Manhattan Press (H.K.) Ltd.

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16.1 Magnetic force and magnetic field (SB p. 108)

Magnetic field magnet produces magnetic field around it

magnetic field lines — show strength & direction of the field © Manhattan Press (H.K.) Ltd.

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16.1 Magnetic force and magnetic field (SB p. 109)

Magnetic field

Expt. 16A Magnetic field of magnet

compass

N

S Plotting magne ti c fi e l d lines

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16.1 Magnetic force and magnetic field (SB p. 109)

Magnetic field Strength: density ↑ → magnetic field strength ↑

Direction: N →S © Manhattan Press (H.K.) Ltd.

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16.1 Magnetic force and magnetic field (SB p. 109)

Magnetic field

bar magnet

iron filings © Manhattan Press (H.K.) Ltd.

plastic board

iron yoke

iron plastic filings slab-shaped magnet board 15

16.1 Magnetic force and magnetic field (SB p. 110)

Magnetic field magnetic field patterns bar magnet

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16.1 Magnetic force and magnetic field (SB p. 110)

Magnetic field magnetic field patterns two bar magnets with unlike poles facing each other

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16.1 Magnetic force and magnetic field (SB p. 110)

Magnetic field magnetic field patterns two bar magnets with like poles facing each other neutral point resultant magnetic field = 0

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16.1 Magnetic force and magnetic field (SB p. 110)

Magnetic field magnetic field patterns slab-shaped magnets

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16.1 Magnetic force and magnetic field (SB p. 111)

Class Practice 2: 1. Refer to Fig. 16.8. Draw the magnetic field lines formed in the following cases. (a) Two bar magnets with the north and Anssouth poles facing each other wer

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16.1 Magnetic force and magnetic field (SB p. 111)

Class Practice 2: (Cont) 1. (b) Two bar magnets with the north and north poles facing each other Ans wer

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16.1 Magnetic force and magnetic field (SB p. 111)

Class Practice 2: (Cont) 1. (c) Two slab-shaped magnets with their north and south poles facing each other Ans wer

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16.1 Magnetic force and magnetic field (SB p. 111)

Class Practice 2: (Cont) 2. For a bar magnet, the magnetic field is the strongest at its poles two _________ . The magnetic field lines are directed north Ans from ___________ (north / south) pole to wer south ______________ (north / south) pole.

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To section 16.2

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16.1 Magnetic force and magnetic field (SB p. 104)

Quiz

1. If a magnet is placed near another magnet, we find that they attract each other. Which of the following statements about the ends of the magnets facing each other is true? C.

Answe Oneris south

pole.

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pole and the other is north 25

16.1 Magnetic force and magnetic field (SB p. 104)

Quiz (Cont)

2. "Earth is a big magnet." Is this statement true?

Ans wer

A. True

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16.1 Magnetic force and magnetic field (SB p. 104)

Quiz (Cont)

3. A bar magnet is cut into two small pieces. Which of the following is true? C. Each of them has south pole and north pole.

Ans wer Return to

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Text

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16.1 Magnetic force and magnetic field (SB p. 105)

Discussion 1:

Explain briefly why chess pieces can be stuck on a chess board (Fig. (a)) and why the outside piece of a window cleaner can be attracted to the piece inside the window (Fig. (b)). Discuss with Ans your classmates. wer

Fig. (a) © Manhattan Press (H.K.) Ltd.

Fig. (b) 28

16.1 Magnetic force and magnetic field (SB p. 105)

Discussion 1: (Cont)

In a magnetic chess game, tiny magnets inside the chess pieces cause them to stick on the metal chess board. The two pieces of the window cleaner are made of magnets. Therefore, moving the piece inside the window can easily move the piece outside and clean the outside of the glass window in the process. Return to

Text © Manhattan Press (H.K.) Ltd.

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16.1 Magnetic force and magnetic field (SB p. 106)

Thinking 1

Must all magnets necessarily have a north Ans pole and a south pole? wer

Yes. Just as any coin has two sides. Poles occur in pair.

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Text © Manhattan Press (H.K.) Ltd.

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16.1 Magnetic force and magnetic field (SB p. 106)

Thinking 2

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Text

How can the dumbbell-shaped object be held in mid-air without any supporting force as shown? What is the trick? We know that inside the dumbbell-shaped object, there is a cylindrical magnet. Ans is another magnet installed inside the There wer base. Two magnets inside the dumbbell-shaped object and the base are of like poles facing each other. Therefore, it would be held in midair due to the repulsion between the like poles. © Manhattan Press (H.K.) Ltd.

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16.1 Magnetic force and magnetic field (SB p. 107)

Activity 1 Compass

Let's start: 1. Tie each magnet in the middle with one end of a string (Fig. (a)). Fig. (a)

2. Four students stand at each corner of the classroom. Each one holds a string with a magnet. © Manhattan Press (H.K.) Ltd.

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16.1 Magnetic force and magnetic field (SB p. 107)

Activity 1 (Cont) Compass

3. Make sure that there are no other magnets nearby. Observe the directions of the Ans magnets. wer All the magnets are aligned in the north-south direction. 4. Draw a floor map of your classroom in Fig. (b) and use the above method to specify the north direction. Return to © Manhattan Press (H.K.) Ltd.

Text

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16.1 Magnetic force and magnetic field (SB p. 108)

Thinking 3

Why is repulsion the only way to test Ans whether a bar is magnet? wer

This is because an iron bar also be attracted by a magnet. Therefore, repulsion is the only sure test.

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Text

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