The table below shows the current in three different electrical appliances when connected to the 240 V mains supply:
Appliance - Current
Kettle - 8.5 A
Lamp - 0.4 A
Toaster - 4.8 A
(a) Which appliance has the greatest electrical resistance? How does the data show this?
(b) The lamp is connected to the mains supply by using a thin, twin-cored cable consisting of live and neutral wires.
State two reasons why this cable should not be used for connecting the kettle to the mains supply.
(c) Calculate the power rating of the kettle when it is operated from the 240 V mains supply.
(d) A man takes the kettle abroad where the mains supply is 120 V. What is the current in the kettle when it is operated from the 120 V supply?
(a) Lamp; because least current is flowing through it.
(b) Large current drawn by the kettle; Earth connection needed.
(c) We know that
P = VI
V = 240V, I = 8.5A
P = 240 x 8.5
= 2040 W = 2.04kW
(d) When connected to 240 V supply, P = 2040W
R = V2/P = 2402/240
R = 28.23 ohm
Now, when V = 120V, R = 28.23 ohm
I = V/R
= 120/28.23
= 4.25A