Power, current, and potential

Electricity is a set of phenomena related to the motion of electrically charged particles [i]. When we measure how much “electricity” is delivered, we measure how much electrical energy is delivered, usually measured in kWh. In this context, “electricity” means “electrical energy”.

Power is the rate of energy transfer, measured in watt. If a consumer switches on an electric device, it consumes electricity at a rate characterized by its power. More powerful devices consume more electricity. If a producer generates electricity with a powerful generator, it can inject electricity in the grid at a high rate. Generators have a minimum and a maximum power at which they can generate electricity.

Since power is the rate at which electric energy is transferred in a circuit, the amount of electrical energy delivered in a time period  is . If you apply more power, you can deliver more electricity in the same period of time.

An electric current is the movement of electric charge. This does not mean that electrons are produced by a generator, travel through a network, and then arrive at a consumer’s device. It means that electrical energy is produced by a generator and travels through a network by local movements of electrons. This is similar to the case where you insert water at one end of a hosepipe that is already full. Water will come out at the other end almost immediately, not because a water molecule travels immediately to the other end of the hosepipe, but because water molecules press each other locally. Electrical energy travels through a network nearly at the speed of light, electrons move through it very slowly.

Electric current is measured in ampere. When a consumer switches off a device, demand in the electricity grid drops, and less current flows through the grid. When a device is switched on, more current flows through the grid.

A potential difference is the work required to move a unit electrical charge a specified distance. It is measured in volt. Voltage produced by a generator is kept constant by regulating the magnetic field in which the coil rotates. Electricity is transported over large distances at high voltage, because the total resistance of the wires is high.

[i] “Electricity,” Wikipedia, https://en.wikipedia.org/wiki/Electricity