Page 108 - Physics 10_Float

CURRENT ELECTRICITY

The time interval after which the a.c voltage or current
repeats its value is known as its time period.

The change in the values of voltage and current corresponds to
the frequency of the source. In Pakistan, alternating current
oscillates 50 times every second. Thus, its frequency is 50 Hz
Alternating current has advantages that make it more Colour coding
practical for use in transferring electrical energy. For this Livewire (L): Red or brown
reason, the current supplied to our homes by power Neutralwire (N): Black or blue
companies is alternating current rather than direct Earthwire (E): Green/yellow
current.

Supply to a House
The electric power enters our house through three
wires. One is called earthwire or ground wire (E). This
carries no electricity. The earthwire is connected to a
large metal plate buried deep in the ground near the
house. The other wire is maintained at zero potential by
connecting it to the Earth at the power station itself and
is called neutral wire (N). This wire provides the return
path for the current. The third wire is at a high potential
Effect of electric
and is called livewire (L). The potential difference currents on the body
between the livewire and the neutral wire is 220V. Current Effect
Our body is a good conductor of electricity through 0.001 A Can be felt
which current can easily pass. Therefore, if a person 0.005 A Is painful
holds livewire, current will start flowing to the ground 0.010 A Causes involuntary
muscle contractions
while passing through his body which may prove fatal for
(spasms)
the person. All electrical appliances are connected 0.015 A Causes loss of muscle
across the neutral and the livewires. The same potential control
difference is therefore applied to all of them and hence 0.070 A Goes through the
these are connected in parallel to the power source. heart; causes serious
disruption; probably
House Wiring fatal if current lasts
for more than 1 s.
Figure 14.16 shows the system of house wiring. The wires
coming from the mains are connected to electricity meter
installed in the house. The output power from the electric
meter is taken to the main distribution board and then to the
domestic electric circuit.
The main box contains fuses of rating about 30 A. A

108 Not For Sale – PESRP