Fuse class 10 | 10th class physics | safe use of electricity | punjab, federal, kpk, balochistan

Fuse 10th class physics chapter 14 | 10th physics chapter 14 safe use of electricity | urdu / hindi
14.14 SAFE USE OF ELECTRICITY IN HOMES
In order to protect persons, devices and property from the
hazards of electricity there is a need of extensive safety
measures in household electricity. Take much care to use
fuses and circuit breakers in an electric circuit as safety
devices. They prevent circuit overloads that can occur when
too many appliances are turned ON at the same time or when
a short circuit occurs in one appliance.
Fuse
A fuse is a safety device that is connected in series with the
livewire in the circuit to protect the equipments when excess
current flows. It is short and thin piece of metal wire that
melts when large current passes through it. If a large, unsafe
current passes through the circuit, the fuse melts and breaks
the circuit before the wires become very hot and cause fire.
Fuses are normally rated as 5 A, 10 A, 13 A,30 A, etc. Different
types of fuses are shown in Fig.14.18.
Following safety measures should be taken while using fuses
in household electrical circuits:
(i) Fuses to be used should have slightly more rating than the
current which the electrical appliance will draw under
normal conditions. For example, for a lightning circuit choose
a 5 A fuse as the current drawn by each lamp is very small
(about 0.4 A for a 100 W lamp). In such circuit, 10 lamps of
100 W can be safely used as the total current drawn is only 4 A
which can be calculated using the formula P = VI.
Fig. 14 .18: Different types of fuses
Identifying Circuit
Components
CURRENT ELECTRICITy

(ii) Fuses should be connected in the livewire so that the
appliance will not operate after the fuse has blown.
(iii) Switch OFF the main before changing any fuse.
Circuit Breaker
The circuit breaker (Fig. 14.19) acts as a safety device in the
same way as a fuse. It disconnects the supply automatically if
current exceeds the normal value. When the normal current
passes through the livewire the electromagnet is not strong
enough to separate the contacts. If something goes wrong
with the appliance and large current flows through the
livewire, the electromagnet will attract the iron strip to
separate the contacts and break the circuit (Fig. 14.20). The
spring then keeps the contacts apart. After the fault is
repaired, the contacts can then be pushed back together by
pressing a button on the outside of the circuit breaker box.
Earthwire
Sometimes, even the fuse cannot capture the high currents
coming from the livewire into the household appliance.
Earthing further protects the user from electric shock by
connecting the metal casing of the appliance to Earth (a wired
connection to the bare ground). Many electrical appliances
have metal cases, including cookers, washing machines and
refrigerators. The Earthwire provides a safe route for the
current to flow through, if the livewire touches the casing
(Fig.14.21). We will get an electric shock if the livewire inside an
appliance comes loose and touches the metal casing.
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