Question

Define electric power. Express it in terms
of potential difference V and resistance R.
(b) An electrical fuse is rated at 2 A. What is
meant by this statement?
(c) An electric iron of 1 kW is operated at
220 V. Find which of the following fuses that
respectively rated at 1A,3 A and 5 A can be
used in it.


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Answer 1

(a)

• Define electric power. Express it in terms of potential difference V and resistance R.
• Electric power is defined as the rate at which energy is dissipated in a circuit.

We know,

• P = work done/time taken
• P = energy dissipated/time
• P = I²Rt/t

Also,

• I = V/R (From ohm's law)
• P = (V/R)² x R x t/t
• P = V²/R² x R x t/t
• P = V²/R

(b)

• An electrical fuse is rated at 2 A. What is meant by this statement?
• This statement means, the maximum current which can flow through the circuit is 2A. If it exceeds, the temperature of the fuse will rise. This will melt the fuse and break the circuit.

(c)

• P = 1kW (1kW = 1000 W)
• V = 220V
• I = P/V
• I = 1000/220
• I = 4.5A

• In the given circuit, a current of 4.5A will flow. Therefore a 5A fuse must be used.