Power in Electric Circuits

Power is defined as the rate at which energy is transferred or transformed. In electrical circuits, it is expressed in Watts (W).
The formula for power is P=IV, where P is power, I is current and V is voltage.
Another formula is P=I²R, where R is resistance. This formula is derived by substituting Ohm’s law (V=IR) into the power formula.
The third formula for power is P=V²/R. This can be derived by substituting Ohm’s law into the power formula too.
Power in an electrical circuit is described as the product of the voltage across a device and the current flowing through it. So, the higher the current and/or voltage, the higher the power.
In terms of energy transfer, if a device has a higher power, it means it is transferring more energy every second.
Electrical appliances have the power rating marked on them which means how much energy they consume per second.

Power Consumption

Power consumed by electrical appliances is generally given in watts (W) or kilowatts (kW). One kilowatt is equal to 1000 watts.
You can calculate the energy consumed by an appliance using the formula E=P*t, where E is the energy (in joules), P is the power (in watts) and t is the time (in seconds).
Energy suppliers usually bill customers in kilowatt-hours (kWh), where 1 kWh is the energy used by a 1 kW device in an hour.
To reduce energy consumption, appliances with lower power ratings should be used, or the appliances should be used for shorter periods.

Power and Resistance

Power is also related to resistance. An increased resistance in a device increases the amount of energy transformed to heat. This may be useful in some appliances (like a heater), but unwanted in others (like a computer).
High power devices, such as heaters, have high resistance since they are designed to convert a lot of electrical energy into heat.
In general, efficient devices are those that convert as much of the electrical energy as possible into a useful form, rather than wasting it as heat.

Hopefully, these points provide a comprehensive overview of power in electric circuits, how it is calculated, and how it relates to energy, resistance and efficiency. Good luck your revision!