7C20m - Kadaran Kuasa, spesifikasi elemen pemanas pada cerek, rintangan berkesan litar siri selari

Diagram 12.1 shows two different circuits connecting to three light bulbs and dry cells. The light bulbs are of the same type and the power supplies are of the same value.
Rajah 12.1 menunjukkan dua litar elektrik yang menyambung tiga mentol dan sel kering. Mentol-mentol tersebut adalah serupa dan nilai bekalan kuasa adalah sama.

(a) What is meant by 12V, 24 W.
Apakah yang dimaksudkan dengan 12V, 24W?

[ 1mark/markah]

(b) State the arrangement of the bulbs for both circuits.When the switch in each circuit is on, all the bulbs will be lighted up. State the circuit in which the bulbs will be brighter. Relate the brightness of the bulbs between Circuit X and Circuit Y to deduce a concept in physics with regard to the resistance, potential difference and the current flows through the bulbs in these circuits.

Nyatakan susunan mentol kedua-dua litar tersebut. Apabila suis dalam setiap litar dihidupkan, mentol-mentol akan bernyala. Nyatakan mentol dalam litar yang mana akan menjadi lebih cerah.
Hubungkaitkan kecerahan mentol dalam Litar X dan Litar Y dengan rintangan, beza keupayaan dan arus yang mengalir dalam mentol untuk, menyimpulkan satu konsep fizik .

[5 marks/markah]

(c) Diagram 12.2 shows an an electric jug used to boil water.
Rajah 12.2 menunjukkan sebuah cerek elektrik yang digunakan untuk memasak air.

Diagram 12.2

Rajah 12.2

Table 12.3 shows the specifications for four wires of the same diameter that can be used as a heating element of an electric kettle.
Jadual 12.3 menunjukkan spesifikasi empat dawai berdiameter sama yang boleh digunakan untuk membuat elemen pemanas sebuah cerek elektrik

You are required to determine the most suitable wire and explain the suitability of the aspects in Table 12.3
Anda diminta mengenalpasti dawai yang paling sesuai dan terangkan kesesuaian aspek-aspek yang tertera di Jadual 12.3

[10 marks/markah]

(d) Diagram 12.4 shows three identical resistors in an electric circuit that is connected to a supply voltage 12V.
Rajah12.4 menunjukkan tiga perintang yang serupa dalam satu litar elektrik yang disambungkan kepada bekalan elektrik 12 V

(i) Calculate the effective resistance in circuit
Hitungkan rintangan berkesan dalam litar itu.

[1mark/markah]

(ii) What is the reading of the voltmeter?
Berapakah bacaan voltmeter ?

[2 marks/markah]

(ii) What is the reading of ammeter?
Berapakah bacaan ammeter ?

[ 1 mark/markah]

Jawapan:

No		Answer	Marks
12	a	If the voltage supplied is 12V the power generated is 24W	1
	b	Circuit X Circuit Y Series parallel Bulbs are dimmer Bulbs are brighter Voltage in each bulb in circuit Y is higher than voltage in each bulb in circuit X Current in each bulb in circuit X is higher than current in each bulb in circuit Y Student describe circuit X or circuit Y / both are accepted	1 1 1 1 1
	c	Specification Reason Density - Low Lighweight / not heavy /portable Melting point - High Does not melt at high temperatures / does not melt easily Rate of oxidation - Low Does not oxidize easily / can be used for a longer period/not rust easily Resistance - high more heat will be produced R is chosen because  it has a low density , high melting point , low rate of oxidation  and it has a high resistance	2 2 2 2 2
	d (i)	Rintangan berkesan = 4 + (4x4)                  4+ 4          = 4 + 2        = 6 Ω	1
	(ii)	V = IR = 2 x 4              = 8 V	1 1
	(iii)	I = 12   = 2A/2  = 1A         6	1
TOTAL			20