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MODUL • Fizik TINGKATAN 5

Latihan / Exercise

1 Stesen kuasa menjana 40 kW kuasa elektrik menggunakan rangkaian penghantaran tenaga berintangan
8 Ω. Berapakah kehilangan kuasa semasa penghantaran akibat rintangan kabel jika tenaga elektrik dihantar pada
A power station generates 40 kW of electric power using a power transmission line with resistance of 8 Ω. What is the power
KBAT dissipated due to the resistance of the transmission cables when the current is transmitted at
(a) 5 000 V (b) 20 kV
Penyelesaian / Solution

(a) Hitungkan nilai arus dalam kabel, I (b) P = I V
Calculate value of current in the cable, I 40 × 10 W = I × (20 × 10 ) V
3
3
3
Kuasa dihantar melalui kabel, P = IV I = 40 × 10 W
3
The power transmitted by the cable, P = IV 20 × 10 V
40 × 10 W = I × 5 000 V = 2 A
3
3
I = 40 × 10 W Maka, kuasa yang hilang disebabkan rintangan,
5 000 V So, the power loss due to the resistance,
= 8 A P = I R
2
Maka, kuasa yang hilang disebabkan rintangan, = (2 A) × 8 Ω
2
So, the power loss due to the resistance, = 32 W
P = I R
2
= (8 A) × 8 Ω
2
= 512 W
UNIT 3
2 Stesen kuasa menjana 80 MW kuasa elektrik pada beza keupayaan 80 kV a.u. melalui rintangan kabel 5 Ω.
A power station generates 80 MW of electric power at a voltage 80 kV through a cable of resistance 5 Ω. Determine:
UNIT 3
(a) kuasa yang hilang semasa penghantaran tenaga melalui kabel.
KBAT
the power loss in the transmission cable.
(b) peratus kuasa yang hilang. / the percentage of the power loss.
(c) kecekapan penghantaran kuasa. / the efficiency of the power transmission.
(d) pengurangan beza keupayaan di dalam kabel. / the voltage drop in the cable.
Penyelesaian / Solution

(a) Hitungkan nilai arus dalam kabel, I (c) Tenaga dihantar = Kuasa dibekal – Kuasa hilang
Calculate value of current in the cable, I Power transmitted = Power supply – Power loss
6
6
Kuasa yang dihantar oleh kabel, P = IV = 80 × 10 W – 5 × 10 W
6
The power transmitted by the cable, P = IV = 75 × 10 W
6
80 × 10 W = I × (80 × 10 V) Kecekapan / So, efficiency = 75 × 10 W × 100%
3
6
6
6
I = 80 × 10 W 80 × 10 W
80 × 10 V = 93.75%
3
= 1 000 A
(d) Pengurangan voltan / Voltage drop = IR
Oleh itu, kuasa hilang akibat rintangan, = 1 000 A × 5 Ω
So, the power loss due to the resistance = 5 000 V
P = I R
2
= (1 000 A) × 5 Ω
2
= 5 × 10 W
6
(b) Peratus kuasa hilang
Percentage of power loss
6
= 5 × 10 W × 100%
80 × 10 W
6
= 6.25%

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03-Physic F5 2018.indd 121 26/08/2019 11:23 AM