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 has the greatest electrical resistance as resistance oppose the flow of current, and the lamp has least amount of current.

(b) According to the given data large amount of current is needed by kettle, so it must be connected to the earthing.


(c) As we know that


P = VI


V = 240V, I = 8.5A


P = 240X8.5 = 2040 W = 2.04 kW


(d) When kettle is connected to 240 V supply, then the P = 2040 W


R = V2/P =


R = 28.23 ohm


Now, when V = 120V, R = 28.23 ohm


I = V/R = 120/28.23 = 4.25A


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