Section 16.1 Magnetic Force and Magnetic Field

8/14/2019 Section 16.1 Magnetic Force and Magnetic Field

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© Manhattan Press (H.K.) Ltd. 1

Section 16.1Section 16.1

Magnetic force andMagnetic force and

magnetic fieldmagnetic field

Section 16.1Section 16.1

Magnetic force andMagnetic force and

magnetic fieldmagnetic field• Permanent magnetPermanent magnet

• Magnetic forceMagnetic force

• Magnetic fieldMagnetic field




Permanent magnet

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

Chinese

discovered

"lodestone"

Go to

Discussion 1Discussion 1

Go to

QuizQuiz

always points in N-S

magnet




S

N

North

points to

Arctic

South

points to

Antarctic

E ve r y ma gne t

ha s no r t h

po le & so u t h

po le

Permanent magnet


Thinking 1Thinking 1




S N N S

S N N SS

N N S

repelrepel

Magnetic force


Like poles repel




S N NS

S N NSS

N NS

attracattractt


Magnetic force

Unlike poles attract




N-poles point to Arctic

Arctic

Antarctic

Arctic

Antarctic


The earth is like magnetGo to

Activity 1Activity 1


Magnetic force





Magnetic force

compass —

indicates direction accurately




magnets attract

paper clips


Magnetic force




iron rod

S N

Iron objects

magnetized


Magnetic force




iron

gold

silver

copper

aluminium

N


Magnetic force


iron

gold

silver

copper

aluminium




Class Practice 1: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 pieceof 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 thepole of the magnet.

(iii) A magnet cannot attract or repel Z at all.

X is _______________________________.

Y is _______________________________.

Z is _______________________________.

Ans

wer


a piece of iron

a magnet

a piece of aluminium




magnet produces magnetic field around it

Magnetic field


magnetic field lines — show strength & direction

of the field




N Scompass

P l o t t i ng m ag ne t i c f i e l d l i ne s

Magnetic field


Expt. 16A

Magnetic field

of magnet

http://movie/Expt%2016A/16A.avi




Direction:

N →S

Strength:

density ↑ →

magnetic field

strength ↑

Magnetic field





Magnetic field


plastic board

plastic

board

bar magnet

iron filings slab-shaped magnet

iron yoke

iron

filings




magnetic field patterns

Magnetic field


bar magnet





Magnetic field


two bar magnets with

unlike poles facing

each other





Magnetic field


two bar magnets with

like poles facing

each other neutral pointresultant

magnetic field = 0





Magnetic field


slab-shaped magnets




Class Practice 2: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 south poles

facing each other Ans

wer





Class Practice 2: (Cont)Class Practice 2: (Cont)

1. (b) Two bar magnets with the north and north poles

facing each other Ans

wer






1. (c) Two slab-shaped magnets with their north and south

poles facing each other Ans

wer






2. For a bar magnet, the magnetic field is the strongest at its

two _________ . The magnetic field lines are directed

from ___________ (north / south) pole to

______________ (north / south) pole.

Answer


poles

north

south




To section 16.2

http://e-ch16_02.ppt/

http://e-ch16_02.ppt/




QuizQuiz

1. If a magnet is placed near another magnet,

we find that they attract each other. Which

of the following statements about the endsof the magnets facing each other is true?

Answe

r C. One is south pole and the other is north

pole.





Quiz (Cont)Quiz (Cont)

2. "Earth is a big magnet."

Is this statement true?Ans

wer

A. True





Quiz (Cont)Quiz (Cont)

3. A bar magnet is cut into two small

pieces. Which of the following is true?

Answer C. Each of them has south pole and

north pole.

Return to

TextText





Discussion 1:Discussion 1:

Explain briefly why chess pieces can be stuck ona 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

your classmates. Answer


Fig. (b)Fig. (a)




Discussion 1: (Cont)Discussion 1: (Cont)

In a magnetic chess game, tiny magnets inside thechess 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 insidethe window can easily move the piece outside and

clean the outside of the glass window in the process.


Return to

TextText





Must all magnets necessarily have a northpole and a south pole? Ans

wer

Return to

TextText

Yes. Just as any coin has two sides.

Poles occur in pair.


i f d i fi ld ( )





How can the dumbbell-shaped object beheld 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

wer

Return to

TextText

There is another magnet installed inside the

base. Two magnets inside the dumbbell-shapedobject and the base are of like poles facing

each other. Therefore, it would be held in mid-

air due to the repulsion between the like poles.


16 1 M i f d i fi ld (SB 107)




Let's start:

1. Tie each magnet in the middle

with one end of a string

(Fig. (a)).

2. Four students stand at each corner of theclassroom. Each one holds a string with a

magnet.

Activity 1Activity 1

CompassCompass


Fig. (a)

16 1 M ti f d ti fi ld (SB 107)




3. Make sure that there are no other magnetsnearby. Observe the directions of the

magnets.

4. Draw a floor map of your classroom in

Fig. (b) and use the above method tospecify the north direction.

Activity 1 (Cont)Activity 1 (Cont)

CompassCompass

All the magnets are aligned in the north-southdirection.

Ans

wer

Return to

TextText


16 1 M ti f d ti fi ld (SB 108)



© Manhattan Press (H K ) Ltd 34


Why is repulsion the only way to testwhether a bar is magnet? Ans

wer

Return to

TextText

This is because an iron bar also be

attracted by a magnet. Therefore,repulsion is the only sure test.


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Section 16.1 Magnetic Force and Magnetic Field