Electricity: Energy and Power in Circuits

• Energy transferred (work done) in a circuit is governed by the formula: Energy = Charge (Q) * Voltage (V), where energy is measured in Joules, charge in Coulombs and voltage in Volts.

• Power in a circuit is referenced as the rate of energy transfer or the rate of work done and is determined by the formula: Power (P) = Voltage (V) * Current (I); Power in Watts, Voltage in Volts, and Current in Amperes.

• Another formula to calculate the power in a circuit is P = I² * R, with I being current and R being resistance.

• The amount of energy an appliance uses is determined by its power rating and the length of time it’s in use. This can be found using the formula: Energy Transferred (E) = Power (P) * Time (t); where power is in Watts, time is in seconds, and energy in Joules.

• The kilowatt-hour (kWh) is a unit of energy commonly used for billing on electricity consumptions. One kWh equals the amount of energy consumed by a 1kW appliance left on for one hour.

• The cost of electrical energy can be calculated using the equation: Total Cost = Number of kWh * Cost per kWh.

• To prevent electric shocks, the earth wire and the fuse or circuit breaker are designed as safety devices within a plug.

• A circuit breaker breaks the circuit when the current is too high, and a fuse is a safety device that melts and breaks the circuit if the current goes above a specific level.

• Appliances with metal cases are much more dangerous because they can easily lead to an electric shock. In these cases, the earth wire is crucial and is connected to the metal case, so the current flows safely to the earth if there is a fault.

• The power of a device represents the energy per unit time that it consumes or provides.-energy-efficient appliances are preferred as they use less energy/power to perform the same task and thereby, save on energy usage and cost.

• Always remember to consider ‘power’ when comparing the efficiency of electrical devices, alongside other factors such as cost, environmental impact, and energy consumption.