Section 16.3 Electromagnet

8/14/2019 Section 16.3 Electromagnet

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Manhattan Press (H.K.) Ltd. 1

Section 16.3Section 16.3

ElectromagnetElectromagnet

Section 16.3Section 16.3

ElectromagnetElectromagnet

Factors affecting the strength ofFactors affecting the strength of

electromagnetelectromagnet


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it works as magnetwhen there is a flow of

I

16.3 Electromagnet (SB p. 117)

Electromagnet

electromagnet

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Discussion 3Discussion 3

can change fieldstrength


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Electromagnet

soft iron

cores

low voltage d.c.power supply

strongly magnetized

demagnetized

switch off


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Expt. 16C

Electromagnet d.c.power supply

soft-iron rod

paper clips

solenoid


Electromagnet
http://movie/Expt%2016C/16C.avi


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electromagnet attractspaper clips


Electromagnet

use compass to finddirection of field


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S N

direction of current reversed


Electromagnet


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Factors affecting the strength of

electromagnet

Thinking 5Thinking 5


Strength of electromagnet

Go to

Discussion 4Discussion 4


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To section 16.4
http://e-ch16_04.ppt/http://e-ch16_04.ppt/


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Discussion 3:Discussion 3:

1. How can you produce a magnetic field otherthan using a permanent magnet?

2. Compare the magnetic field produced in step 1

with that produced from a permanentmagnet. Which one is more practical? Why?

Discuss with your classmates.Ans

wer1. Pass a current through a conducting wire.


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2. The method we suggested is more practical because

we can change the polarity and strength of the

electromagnet easily.


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Thinking 5Thinking 5

Which of the following can increase the strengthof the electromagnet in the figure?

(a) Replace the steel rod with a soft iron rod.

(b) Replace the resistor with the one of lowerresistance.

(c) Decrease the number of turns in the solenoid.

Answer

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(a) and (b). In (b), the current

increases if the resistance of

the resistor decreases.



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Discussion 4:Discussion 4:

Fig. (a) shows the structure of a typical electric

bell. How does it work? Explain briefly.

Ans

wer


Fig. (a) Fig. (b)


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Discussion 4: (Cont)Discussion 4: (Cont)

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 toproduce 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.


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Section 16.3 Electromagnet

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