Question

Fuse 3A, 5A and 10A are available. Calculate and select the fuse for operating an electric iron of power 1 KW at a 220 V line?

I calculated and got 0.45A but it is not in the fuses given

Plz explain why I am wrong?

Answer 1

A Fuse prevents extra voltage from going into the appliance.


Sometimes there can be a short circuit. More voltage and hence more current flows into the appliance than what it can handle. This can damage the electrical appliance and can even cause a fire. 

To prevent this overloading, a fuse is kept as a safety measure. 

A Fuse stops current flow if it goes beyond a certain limit.

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Here we are given an electrical iron, and our data is:

$P = 1 \, \, kW = 1000 \, \, W \\ \\ V = 220 \, \, V$

From this, we can find the Current at which the Electric Iron is supposed to operate.

$P = VI \\ \\ \implies I = \frac{P}{V} \\ \\ \implies I = \frac{1000}{220} \\ \\ \implies \boxed{I \approx 4.545 \, \, A}$

Thus, the iron is supposed to function at a current of approximately 4.5 amperes. 

If the current is much more than 4.5 amperes, the electric iron can get damaged.

We cannot use a fuse of 3 A. It would prevent the iron from operating at its desired capacity.

We also cannot use a 10 A fuse. It wouldn't provide protection if the current becomes, say, 7 A or 8 A.


Thus, We must use the 5 A fuse. It will protect the iron from voltage and current overloading.

In your calculations, you must have taken an improper value of Power, something like 100 watts, which gave you your answer. You probably missed that 1 kilowatt = 1000 watts.


Finally, Answer is 5 A fuse.

Answer 2

"Answer: The formula is I = P/E, where P = power, I = current and E = electromotive force in volts.

P = 1 kw = 1000 watt

V = 220 volts

Therefore,

I = 1000/220 = 4.5 ampere (A).

0.45 A is the wrong answer because the calculation was wrong.

"