ELECTRICAL ENERGY

ELECTRICAL ENERGY
Key notes:
1. In a household circuit, the three wire are the live wire, the netral wire and the
earth wire.
2. Fuses and switches are placed in the live wire.
3. The earth wire is connected to the metal casing of the appliance.
4. A fuse is suitable for use if its current rating is slightly higher than the normal
operating current.
5. For an appliance which has double insulation, the inside metal wall is covered
with an insulating sheet so that if a live wire becomes loose and touches the
inside wall, current will not leak out of the wall.
6. Appliances are wired to three-pin plugs which are in turn plugged into wall
sockets.
7. In a three-pin plug, a fuse is connected to the live wire.
8. Electricity is use in lighting, heating and motors.
9. When current flows through the filament of a bulb, heat and light are
dissipated.
10. A greater percentage of electrical energy is converted into light in a
fluorescent lamp when compared to a filament lamp.
11. Heating elements of heaters are made of Nichrome wire.
12. Motors are used to convert electrical energy into mechanical energy.
13. The main source of dangers of electricity are
a) damp conditions
b) overheating of cables
c) Damaged insulation
Formulas:
 Power dissipated, P = IV
P = I²R
P = V² / R
 Electrical energy = IVt
O LEVEL PHYSICS REVISION NOTES
= I²Rt
= (V²/R)
 THE COST OF ELECTRICAL ENERGY
1 kWh = 1 kilowatt x 1 hour
= 1000watt x 1 hour
= (1000 J/s) for 1 hour
= (1000 J/s) x (60 x 60s)
= 3.60 x 10(*6)J *power of 6
 Cost of electricity consumption = (total kWh) x (cost per kWh