Revision: Electricity >> Household Electricity Physics ICSE ICSE Class 8 CISCE

An electric fuse is a safety device which is used to limit the current in an electric circuit. The use of a fuse safeguards the circuit and the appliances connected in that circuit from being damaged.

The unit in which the consumer pays the cost of electrical energy consumed is kWh.

Current Rating of Fuse in a Circuit = \[\frac{\text{total power of appliances in circuit}}{\text{voltage of the supply}}\]

R = \[\frac {V^2}{P}\]

or

R = \[(\text{voltage rating on the appliance})^2 \over \text{power rating on the appliance}\]

Energy (in kWh) = power (in kW) × time (in h)

= \[\frac{\text{power (in watt)}\times\text{time (in hour)}}{1000}\]

= \[\frac{V(\mathrm{volt})\times I(\mathrm{ampere})\times t(\mathrm{hour})}{1000}\]

Cost of electricity = electrical energy in kWh × cost per kWh

• Electric power is generated at 11 kV and transmitted at very high voltage because high voltage results in low current and hence less energy loss due to heating in transmission lines.
• Alternating current (50 Hz) is used since its voltage can be stepped up and stepped down using transformers, which is not possible with d.c.
• The voltage is stepped down in stages from 132 kV → 33 kV → 11 kV → 220 V before supplying electricity to domestic consumers.

• Each electric appliance is provided with a three-core flexible cable consisting of live, neutral, and earth wires.

• The colour coding of the wires is fixed: red (or brown) for live, black (or light blue) for neutral, and green for earth wire.

• Watt-hour (Wh) and kilowatt-hour (kWh) are the commercial units of electrical energy, used instead of joule for practical purposes.
• Electrical energy consumed by household and industrial appliances is measured in kilowatt-hours (kWh) and used to calculate electricity costs.
• One kilowatt-hour represents a large amount of energy, equivalent to the energy used by a high-power appliance in one hour.