Section 16.3 Electromagnet

Section 16.3 Electromagnet • Factors affecting the strength of electromagnet

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16.3 Electromagnet (SB p. 117)

Electromagnet

electromagnet • it works as magnet when there is a flow of • Ican change field strength Go to © Manhattan Press (H.K.) Ltd.

Discussion 3

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16.3 Electromagnet (SB p. 118)

Electromagnet low voltage d.c. power supply

switch off

soft iron cores

demagnetized strongly magnetized © Manhattan Press (H.K.) Ltd.

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16.3 Electromagnet (SB p. 118)

Electromagnet Expt. 16C Electromagnet

d.c.power supply soft-iron rod solenoid

paper clips

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16.3 Electromagnet (SB p. 119)

Electromagnet electromagnet attracts paper clips

use compass to find direction of field © Manhattan Press (H.K.) Ltd.

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16.3 Electromagnet (SB p. 119)

Electromagnet S

N

direction of current reversed

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16.3 Electromagnet (SB p. 119)

Factors affecting the strength of electromagnet

Strength of electromagnet ↑

Thinking 5 © Manhattan Press (H.K.) Ltd.

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Discussion 4

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To section 16.4

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16.3 Electromagnet (SB p. 117)

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Discussion 3:

Text 1. How can you produce a magnetic field other than using a permanent magnet? 2. Compare the magnetic field produced in step 1 with that produced from a permanent magnet. Which one is more practical? Why? Discuss with your classmates. Ans a conducting wire. 1. Pass a current through wer

2. The method we suggested is more practical because we can change the polarity and strength of the electromagnet easily. © Manhattan Press (H.K.) Ltd.

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16.3 Electromagnet (SB p. 119)

Thinking 5

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Text

Which of the following can increase the strength of the electromagnet in the figure? (a) Replace the steel rod with a soft iron rod. (b) Replace the resistor with the one of lower resistance. (c) Decrease the number of turns in the solenoid. Ans (a)wer and

(b). In (b), the current increases if the resistance of the resistor decreases. © Manhattan Press (H.K.) Ltd.

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16.3 Electromagnet (SB p. 120)

Discussion 4:

Fig. (a) shows the structure of a typical electric bell. How does it work? Explain briefly.

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

Ans wer

Fig. (b) 11

16.3 Electromagnet (SB p. 120)

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Discussion 4: (Cont)

Text

When the push button is pressed, a current flows through the circuit and the electromagnet magnetizes the soft-iron armature which forms a part of the handle of the hammer. The hammer is then attracted by the electromagnet and hits the gong to produce a sound. At the same time, the contact breaks the circuit at A. Then the spring pulls the hammer back to its original position and the circuit is closed again. The whole process repeats itself as long as the button is pressed. It allows the bell to ring continuously. © Manhattan Press (H.K.) Ltd.

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