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MODUL • Fizik TINGKATAN 5

2 Rajah menunjukkan 12 V, 36 W mentol menyala dengan 4 Rajah menunjukkan 12 V, 48 W mentol menyala dengan
kecerahan normal apabila disambungkan kepada bekalan kecerahan normal apabila disambungkan kepada bekalan
kuasa 240 V melalui transformer. Bilangan lilitan gegelung kuasa 240 V melalui transformer.
primer ialah 500. The diagram shows a 12 V, 48 W bulb light up with
The diagram shows a 12 V, 36 W bulb light up with normal normal brightness when it is connected to a 240 V mains
brightness when it is connected to a 240 V mains supply supply through a transformer.
through a transformer. The number of turns of the primary 0.3 A
coil is 500.

240 V 12 V, 36 W 240 V 12 V, 48 W

Berapakah bilangan lilitan gegelung sekunder? N = 200
s
What is the number of turns of the secondary coil? Hitungkan / Calculate
Penyelesaian / Solution (a) bilangan lilitan gegelung primer.
the number of turns of the primary coil.
Diberi / Given V = 12 V, V = 240 V, N = (b) arus dalam gegelung sekunder.
p
p
s
500 lilitan / turns the current in the secondary coil.
N s = V s (c) kecekapan transformer.
N p V p the efficiency of the transformer.
12 V
N s = Penyelesaian / Solution
500 lilitan / turns 240 V
12 V × 500 lilitan / turns Diberi / Given V = 240 V, N = 200 lilitan / turns,
p
s
N =
s 240 V V = 12 V, I = 0.3 A
s
p
= 25 lilitan / turns UNIT 3
(a) N s = V s
N p V p
UNIT 3
3 Transformer injak-turun disambungkan ke bekalan kuasa 200 lilitan / turns = 12 V
240 V dan memberikan kuasa 90 W kepada komputer N p 240 V
riba, 30 V. 240 V × 200 lilitan / turns

KBAT [Andaikan transformer adalah unggul.] N = 12 V
p
A step-down transformer connected to 240 V mains power N = 4 000 lilitan / turns
supply delivers 90 W of power at 30 V to a notebook computer. p
[Assume that the transformer is ideal.] (b) V = 12 V, P = 48 W
Hitungkan / Calculate s P s s 48 W
(a) arus dalam gegelung sekunder. \ I = = 12 V = 4.0 A
s
the current in the secondary coil. V s
(b) arus dalam gegelung primer. (c) Kuasa output / Output power = 48 W
the current in the primary coil.
Penyelesaian / Solution Kecekapan / Efficiency = P output × 100%
Diberi / Given V = 240 V, P output = 90 W, V = 30 V P input
s
p
48 W
(a) P = I V (b) I V = I V = × 100%
output s s p p s s I p V p
90 W = I × 30 V I × 240 V = 3 A × 30 V 48 W
s p 90 W = 0.3 A × 240 V × 100%
I = 90 W I = 240 V = 66.67%
p
s
30 V
I = 3 A = 0.375 A
s
atau
Kuasa input = Kuasa output
Input power = Output power
Jadi, / Therefore,
I V = 90 W
p
p
\ I = 90 W
p 240 V
I = 0.375 A
p

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03-Physic F5 2018.indd 114 26/08/2019 11:23 AM