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Physics

Domestic Electric Circuits

A 3-pin mains...

Question

A 3-pin mains plug is fitted to the cable for a 1 kW electric kettle to be used on a 250 V a.c. supply. Which of the following statements is not correct?

(a) The fuse should be fitted in the live wire
(b) A 13 A fuse is the most appropriate value to use
(c) The neutral wire is coloured black
(d) The green wire should be connected to the earth pin.

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Solution

(b) A 13 A fuse is the most appropriate value to use.

Given:
P = 1 kW = 1000 W
V = 250 V
∴ Current, I = P/V = 1000/250 = 4 A
Because the current drawn is 4 A, a fuse of 13 A cannot be considered the most appropriate.

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Similar questions

Which one of the following statements is not true ?

(a) In a house circuit, lamps are used in parallel.

(b) Switches, fuses adn circuit breakes should be placed in the neutral wire

(d) When connecting a three-core cable to a 13 A three-pin plug, the red wire goes to the live pin.

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

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(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.

(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 power circuit uses a cable having three different wires.

(a) Name the three wires of the cable.

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(d) To which wire should the switch and fuse be connected?

Q. The table below shows the current in three different electrical appliances when connected to the 240 V mains supply:

Appliance	Current
Kettle	08.5 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 natural 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 main takes the kettle abroad where the mains supply is 120 V. What is the current is the kettle when it is operated from the 120 V supply?

Write true or false for each statement:

(a) A fuse wire has a high melting point.

(b) Flow of protons constitutes electric current.

(d) S.I. unit and commercial unit of electrical energy are same.

(e) Overloading of electric current in circuits can lead to short circuiting.

(f) Our body can pass electricity through it.

(g) The metallic cases of all appliances are insulators of electricity.

(h) The earth wire protects us from an electric shock.

(i) A switch should not be touched with wet hands.

(j) All electrical appliances in a household circuit work at the same voltage.

(k) In a cable,the green wire is the live wire.

(l) A fuse is connected to the live wire.

(m) A switch is connected to the neutral wire.

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(b) A 13 A fuse is the most appropriate value to use. Given: P = 1 kW = 1000 W V = 250 V ∴ Current, I = P/V = 1000/250 = 4 A Because the current drawn is 4 A, a fuse of 13 A cannot be considered the most appropriate.

(b) A 13 A fuse is the most appropriate value to use.

Given:
P = 1 kW = 1000 W
V = 250 V
∴ Current, I = P/V = 1000/250 = 4 A
Because the current drawn is 4 A, a fuse of 13 A cannot be considered the most appropriate.