Page 39 - CHAPTER-1 (Electricity)

CHAPTER 1

ELECTRICITY

The filament is isolated thermally, and the bulb is filled with chemically

inactive nitrogen and argon gas to prolong the life of the bulb filament.

b. Electric Fuse:

It is used as an important safety device in household circuits. It also

protects the circuits by terminating the flow of any unduly high

electric currents. The fuse is always connected in series with the mains

supply. A fuse consists of an alloy of lead and tin, which has an

appropriate melting point.

When the current flowing in the circuit exceeds the safe limit, the

temperature in the fuse wire, the fuse wire quickly melts and breaks

the circuit. This helps to protect the other circuit elements from

hazards caused by the heavy current. Fuses are always rated for

different current values such as 1A, 2A, 5A, 10A, 15A, etc.

(iii) Electric Power

It is defined as the amount of electric energy consumed in a circuit per

unit time.

If is the amount of electric energy consumed in a circuit in seconds,

then the electric power is given by:

W
P= But = electric energy =Vq=VIt
t
VIt
∴P= ⟹ P=VI
t

According to Ohm’s law, V=IR

V 2
2
∴P=IR×I=I R ⟹P=
R
The SI unit of electric power is watt (W).

It is said to be 1 watt, if 1 ampere current flows through a circuit having

1-volt potential difference.

i.e. 1 watt = 1 volt × 1 ampere = 1 VA

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