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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
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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
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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
16.1 Magnetic force and magnetic field (SB p. 106)
Thinking 1Thinking 1
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S N N S
S N N SS
N N S
repelrepel
Magnetic force
16.1 Magnetic force and magnetic field (SB p. 106)
Like poles repel
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S N NS
S N NSS
N NS
attracattractt
16.1 Magnetic force and magnetic field (SB p. 106)
Magnetic force
Unlike poles attract
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N-poles point to Arctic
Arctic
Antarctic
Arctic
Antarctic
Thinking 2Thinking 2
The earth is like magnetGo to
Activity 1Activity 1
16.1 Magnetic force and magnetic field (SB p. 106)
Magnetic force
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16.1 Magnetic force and magnetic field (SB p. 107)
Magnetic force
compass —
indicates direction accurately
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magnets attract
paper clips
16.1 Magnetic force and magnetic field (SB p. 107)
Magnetic force
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iron rod
S N
Iron objects
magnetized
16.1 Magnetic force and magnetic field (SB p. 108)
Magnetic force
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iron
gold
silver
copper
aluminium
N
16.1 Magnetic force and magnetic field (SB p. 108)
Magnetic force
Thinking 3Thinking 3
iron
gold
silver
copper
aluminium
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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
16.1 Magnetic force and magnetic field (SB p. 108)
a piece of iron
a magnet
a piece of aluminium
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magnet produces magnetic field around it
Magnetic field
16.1 Magnetic force and magnetic field (SB p. 108)
magnetic field lines — show strength & direction
of the field
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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
16.1 Magnetic force and magnetic field (SB p. 109)
Expt. 16A
Magnetic field
of magnet
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Direction:
N →S
Strength:
density ↑ →
magnetic field
strength ↑
Magnetic field
16.1 Magnetic force and magnetic field (SB p. 109)
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Magnetic field
16.1 Magnetic force and magnetic field (SB p. 109)
plastic board
plastic
board
bar magnet
iron filings slab-shaped magnet
iron yoke
iron
filings
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magnetic field patterns
Magnetic field
16.1 Magnetic force and magnetic field (SB p. 110)
bar magnet
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magnetic field patterns
Magnetic field
16.1 Magnetic force and magnetic field (SB p. 110)
two bar magnets with
unlike poles facing
each other
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magnetic field patterns
Magnetic field
16.1 Magnetic force and magnetic field (SB p. 110)
two bar magnets with
like poles facing
each other neutral pointresultant
magnetic field = 0
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magnetic field patterns
Magnetic field
16.1 Magnetic force and magnetic field (SB p. 110)
slab-shaped magnets
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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
16.1 Magnetic force and magnetic field (SB p. 111)
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Class Practice 2: (Cont)Class Practice 2: (Cont)
1. (b) Two bar magnets with the north and north poles
facing each other Ans
wer
16.1 Magnetic force and magnetic field (SB p. 111)
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Class Practice 2: (Cont)Class Practice 2: (Cont)
1. (c) Two slab-shaped magnets with their north and south
poles facing each other Ans
wer
16.1 Magnetic force and magnetic field (SB p. 111)
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Class Practice 2: (Cont)Class Practice 2: (Cont)
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
16.1 Magnetic force and magnetic field (SB p. 111)
poles
north
south
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To section 16.2
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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.
16.1 Magnetic force and magnetic field (SB p. 104)
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Quiz (Cont)Quiz (Cont)
2. "Earth is a big magnet."
Is this statement true?Ans
wer
A. True
16.1 Magnetic force and magnetic field (SB p. 104)
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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
16.1 Magnetic force and magnetic field (SB p. 104)
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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
16.1 Magnetic force and magnetic field (SB p. 105)
Fig. (b)Fig. (a)
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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.
16.1 Magnetic force and magnetic field (SB p. 105)
Return to
TextText
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Thinking 1Thinking 1
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.
16.1 Magnetic force and magnetic field (SB p. 106)
i f d i fi ld ( )
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Thinking 2Thinking 2
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 Magnetic force and magnetic field (SB p. 106)
16 1 M i f d i fi ld (SB 107)
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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
16.1 Magnetic force and magnetic field (SB p. 107)
Fig. (a)
16 1 M ti f d ti fi ld (SB 107)
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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 Magnetic force and magnetic field (SB p. 107)
16 1 M ti f d ti fi ld (SB 108)
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Thinking 3Thinking 3
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.
16.1 Magnetic force and magnetic field (SB p. 108)
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