Section 15.1 Electric Circuit

Section 15.1 Electric circuit • Electric current • Circuit diagram

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15.1 Electric circuit (SB p. 37)

Electric circuit

In modern cities like HK → demands huge amount of electricity Go to © Manhattan Press (H.K.) Ltd.

Quiz

Go to

Discussion 1

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15.1 Electric circuit (SB p. 38)

Electric circuit Electric circuit a conducting path that electric charges flow through conditions for a bulb to glow: • power source • closed circuit © Manhattan Press (H.K.) Ltd.

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15.1 Electric circuit (SB p. 38)

Electric circuit Open circuit battery copper wires

e− move randomly → no electric current produced switch is open

light bulb © Manhattan Press (H.K.) Ltd.

remains unlit 4

15.1 Electric circuit (SB p. 38)

Electric circuit Closed circuit battery copper wires

e− move in one direction → electric current produced switch is closed

light bulb © Manhattan Press (H.K.) Ltd.

glow 5

15.1 Electric circuit (SB p. 39)

Electric current

dome

earth socket

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light-beam galvanometer

Electric current between the dome & earth → flow of electric charges

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15.1 Electric circuit (SB p. 39)

Electric current electron flow

CAL Workshop 1 Current

conventional current

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15.1 Electric circuit (SB p. 40)

Electric current electric current (I)

Quantity of charge flow Electric current = Time taken Q i.e. I = t

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unit: ampere (A) quantity of charge (Q)

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time (t) © Manhattan Press (H.K.) Ltd.

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15.1 Electric circuit (SB p. 40)

Measuring electric current 1 A = 1 C s -1 1 mA (milliampe re) = 10 -3 C s -1

1μ A (microampe re) = 10 -6 C s -1

ammeter © Manhattan Press (H.K.) Ltd.

milliammeter

microammeter 9

15.1 Electric circuit (SB p. 41)

Measuring electric current Measuring current through light bulb → ammeter connected in series with light bulb

+ terminal of battery

+ terminal of ammeter

Thinking 1 © Manhattan Press (H.K.) Ltd.

ammeter

light bulb 10

15.1 Electric circuit (SB p. 41)

Measuring electric current Typical currents in some electrical appliances Electrical appliance

Typical current

Electric water heater

14 A

Air conditioner

10 A

Hair dryer

3A

TV set

0.8 A

100 W light bulb

0.5 A

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15.1 Electric circuit (SB p. 41)

Circuit diagram Circuit diagram — represent real circuit connection for convenience

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15.1 Electric circuit (SB p. 42)

Circuit diagram Circuit symbols for some electrical components

battery

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light bulb

switch

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15.1 Electric circuit (SB p. 42)

Circuit diagram

ammeter

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voltmeter

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15.1 Electric circuit (SB p. 42)

Circuit diagram

resistor

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rheostat

potential divider

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15.1 Electric circuit (SB p. 42)

Class Practice 1: Fig. (a) shows an electric circuit. Draw its circuit diagram in Fig. (b). Ans wer

Fig. (a)

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To section 15.2

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15.1 Electric circuit (SB p. 36)

Quiz

1. When you switch on a lamp, which of Answe the following is true? r

B. The current flowing out of the light bulb is equal to that into it. © Manhattan Press (H.K.) Ltd.

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15.1 Electric circuit (SB p. 36)

Quiz (Cont)

2. In a classroom, when a fluorescent tube fails, the other fluorescent tubes still light up. In which circuit are they Ans connected? wer B. Parallel circuit © Manhattan Press (H.K.) Ltd.

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15.1 Electric circuit (SB p. 36)

Quiz (Cont)

3. When you connect two identical light bulbs A and B with a battery as shown, which of the following is Ans true? C. Bulb A and bulb B have the same brightness. © Manhattan Press (H.K.) Ltd.

wer Return to

Text

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15.1 Electric circuit (SB p. 37)

Discussion 1:

Which of the following can you use to light up a light bulb? Discuss with your classmates. A. a light bulb and two connecting wires B. a light bulb and a dry cell C. a light bulb, a dry cell and two connecting wires C Ans wer

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15.1 Electric circuit (SB p. 37)

Discussion 1: (Cont)

Explain briefly why the light bulb lights up. Ans wer

In a closed circuit, the dry cell provides a voltage to drive a current passing through the light bulb. Return to

Text

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15.1 Electric circuit (SB p. 41)

Return to

Text

Thinking 1

If the positions of the ammeter and light bulb in Fig. 15.7 are exchanged (Fig. (a)), what happens to the current in the circuit? Ans The currents are the same. Since there is only one path for the current to flow, the value ofwer the current is the same in the whole circuit. Fig. 15.7

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Fig. (a)

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