Page 85 - Physics_Form_2

Current electricity

The live mains lead indicator, commonly Connections should be made firm
called a tester, is made up of a form of a and/or cleaned of rust and other dirt.
screwdriver with a hollow insulating handle
containing a tiny neon discharge tube. One Repairs in electrical appliances
electrode of the neon tube is usually in contact should be limited to connections
with the metal probe of the screwdriver. The to the power supply only. Beyond
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other is connected to the metal cap of the that, an electrical technician should
handle through a high-carbon resistor. When be consulted. Care should be taken
one inserts the metal probe into a live socket to avoid electric shocks during such
and touches a metal cap with a finger, current repairs. Simple repairs on electrical
leaks to the earth through the body and the connections in a domestic system
neon tube glows. Owing to the high resistance, can also be carried out. When a fuse
this current is very low, so there is no risk of blows, it is very likely to be due to
electric shock. Figure 2.53 shows a typical a fault in an appliance. If the fault
tester. is detected and corrected, then the
fuse can be replaced (or the circuit
breaker switched ON).

Other faults occur due to wire cutting
Figure 2.53: Live mains lead indicator(tester) or joining, sockets getting dirty and
switch breakage. All repairs should
Most of the faults that occur in electrical be done with the mains switched
appliances are simple and can be repaired OFF. When replacing switches and
easily. If, for example, an electric kettle fails sockets, the colour code should be
to work, the first thing to check is whether followed strictly.
there is power in the socket. This is done
using the tester. The next step is to check the Exercise 2.4
cable from the socket to the appliance. The
plug should be opened to check the fuse if 1. Explain the properties and
no fault is detected. Also, check each cable functions of a fuse. How does
for continuity using a multimeter. If these a fuse in a lighting circuit differ
components function correctly, the heating from that in a heating or power
element is the next thing to check for faults. circuit? What is the importance
This can be checked for continuity or short of using a fuse in an electrical
circuits using a multimeter. appliance?
2. (a) A refrigerator is marked
If the element is faulty, it must be replaced, 250 V; 400 W. Calculate
as repair may not be possible. If the element the maximum current that
is not faulty, then look for loose connections. can flowthrough it.

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Physics Form 2 Final.indd 79 25/10/2025 10:26