Bab 7

ELECTRICITY 1. Diagram 8.1 shows an electric kettle with specification of 240 V, 1.2 kW.

DIAGRAM 8.1 (a) What is meant by the label 240V, 1.2 kW? ………………………………………………………………………………… ………………………………………………………………………..[1 mark] (b) Calculate (i) the current flows through the electric kettle.

[2 marks] (ii) the resistance of the heating elements in the kettle. [2 marks]

(c) Four electric kettles W, X , Y and Z with specification 240 V, 2 kW are made from the materials with different characteristics. Table 8.1 shows the characteristics of the materials. Kettle

W X Y Z

The characteristics of the materials are used in the heating element in the kettle Boiling Resistivity/10-8 o point/ C Ωm 3501 13.5 1085 5.2 3387 12.4 1064 4.63

Fuse 8A 10 A 10 A 8A

TABLE 8.1

(i) Based on the characteristics of the heating elements in Table 8.1, suggest two electric kettles are suitable to heat water. Give the reason for your answer. …..………………………………………………………………………………… …..………………………………………………………………………………… ..…………………………………………………………………………[3 marks] (ii) Based on the fuse used in the Table 8.1 , suggest two electric kettles are suitable to heat water. Give the reason for your answer. ..…………………………………………………………………………………… ..………………………………………………………………………… [2marks] (iii) Using your answer in (b)(i) and (b)(ii), suggest which electric kettle is the most suitable to heat water. Give the reason for your answer. …..………………………………………………………………………………… …………………..………………………………………………………[2 marks]

(iii)

……………………………………………………………………… ………………………………………………………. [1mark] What is the resistance of the diode when the potential difference is 2 V?

[2marks] 2. (a) State Ohm’s Law ………………………………………………………[1mark] (b) Diagram 8.1 shows a graph of current, I, against potential difference,V, of a diode.

(c) Identical light bulbs, each of resistance R Ω, are connected in three circuits as shown in Diagram 8.2.

The rheostat in each circuit is adjusted and the potential difference,V, against current,I, graphs are plotted for each circuit. The graph for each circuit is shown in diagram 8.3.

(i) (ii)

State whether the ohm’s law is obeyed by the diode. …………………………………………………………….[1mark] Give a reason why there is no current flowing through the diode when the potential difference is between 0V and -2V.

(i)

Match the graphs K, L and M to the circuits X, Y and Z. Circuit

Graph

X Y Z (ii)

(iii)

[3marks] Explain your answers in (c)(i) …………………………………………………………………… ……………………………………………………………… [2marks] Calculate the value of R. [2mark s]