Practical electricity
AQEEL UR REHMAN
O LEVEL PHYSICS
4.4.1 Uses of electricity
1 State common uses of electricity, including heating, lighting, battery charging and powering motors and electronic systems
2 State the advantages of connecting lamps in parallel in a lighting circuit
3 Recall and use the equation power = current × voltage P = IV
4 Recall and use the equation energy = current × voltage × time E = IVt
5 Define the kilowatt-hour (kWh) and calculate the cost of using electrical appliances where the energy unit is the kWh
4.4.2 Electrical safety
1 State the hazards of:
◦ (a) damaged insulation
◦ (b) overheating cables
◦ (c) damp conditions
◦ (d) excess current from overloading of plugs, extension leads, single and multiple sockets when using a mains supply
2 Explain the use and operation of trip switches and fuses and choose appropriate fuse ratings and trip switch settings
3 Explain what happens when a live wire touches a metal case that is earthed
4 Explain why the outer casing of an electrical appliance must be either non-conducting (double-insulated) or earthed
5 Know that a mains circuit consists of a live wire (line wire), a neutral wire and an earth wire and explain why a switch must be connected into
the live wire for the circuit to be switched off safely
6 Explain why fuses and circuit breakers are connected into the live wire
Heating effect of electricity
Electrical power
P = IV
E = IVt
P=I2R
E=I2Rt
Some more symbols
Unit and cost of electrical energy
Unit of energy = joule
Joule = watt x sec this is a small unit
Unit of energy = Kw h
Hazards
Damaged insulation
Overheating of cables
Damp conditions
Fuse https://www.youtube.com/watch?v=S8lB2kxT1n0
It works on the heating effect of current.
It is small wire which melts at higher current than required and
breaks the circuit.
It is used to limit the amount of current.
It is connected in series with live wire so that when fuse blows
away the appliance is at zero volt.
Its rating is slightly above the normal current.
https://www.youtube.com/watch?v=0OKTejgaWTY
Live and neutral wire
Live wire is wire with high voltage/energy charges
Neutral wire is wire with low energy charges. It is used to provide
potential difference or to complete the circuit.
Earth wire
It is earthed at ground in our own place. It is at zero volts and used is used as a safety device.
It is connected with metal casing.
In case a fault arises and metal casing becomes live huge amount of current flows through live
and earth wire and fuse blows up making us safe.
Example
What is the appropriate choice of fuse for a
mains appliance with a power rating of
P = IV
330 W?
V = 230V
P = 330W
P
I = I =?
V
Circuit Breaker
A circuit breaker is an electrical safety device designed to protect
an electrical circuit from damage caused by an overcurrent or short
circuit.
Its basic function is to interrupt current flow to protect equipment
and to prevent the risk of fire.
Unlike a fuse, which operates once and then must be replaced,
a circuit breaker can be reset (either manually or automatically) to
resume normal operation.
