Electrical basics · Lesson 1 of 13
Before you pick up a screwdriver or a multimeter, you only need to understand 4 words: voltage, current, resistance and power. We will explain them with water in pipes, and then work out an electricity bill ourselves.
Inside every copper wire there are tiny particles called electrons. When we connect the wire to a battery or to the mains, these electrons move along the wire around a closed loop. That movement is electric current.
The easiest way to understand it: imagine the wire is a pipe and electricity is water flowing through it.
| Electricity | Measured in | Like what in water |
|---|---|---|
| Voltage | volt V | The pressure that pushes the water (a higher tank gives more pressure) |
| Current | ampere A | The amount of water passing through the pipe every second |
| Resistance | ohm Ω | A narrowing in the pipe that reduces the water getting through |
| Power | watt W | The work the water does (like turning a turbine) |
Everything around us is made of tiny atoms. At the centre of the atom is a positive (+) nucleus, and around it negative (−) electrons orbit.
In metals like copper, the outermost electron of each atom is only loosely held, so it moves easily between atoms. It is called a free electron. A wire is full of countless free electrons moving at random. As soon as we connect a battery, the voltage pushes them all in one direction: that is the current.
More detail later: voltage and current in lesson 2, and why some materials conduct and others don’t in lesson 3.
Move the voltage and resistance sliders and watch both at once: the tank and pipe on top, the battery and lamp below. Notice the speed of the flow and the brightness of the lamp.
This is Ohm’s law: current (amps) = voltage (volts) ÷ resistance (ohms). You will see it at work in lesson 4 (series and parallel), and use it to choose the cable and breaker in lesson 11.
Every appliance has its power in watts (W) written on the nameplate (the sticker with its ratings). Power = voltage × current:
Household mains here is 220 volts, so you can work out the current an appliance draws: I = P ÷ 220.
| Appliance | Power (approx.) | Current at 220V |
|---|---|---|
| LED lamp | 10 W | 0.05 A |
| Phone charger | 20 W | 0.1 A |
| Ceiling fan | 75 W | 0.34 A |
| Fridge | 150 W | 0.7 A |
| Iron | 1200 W | 5.5 A |
| 1.5 HP air conditioner | 1400 W | 6.4 A |
| Water heater | 2000 W | 9.1 A |
| Kettle | 2200 W | 10 A |
You will study power in detail in lesson 5. 1 kilowatt (kW) = 1000 watts. A mechanical horsepower (HP) is about 746 watts, but a "1.5 HP" air conditioner is a cooling size; its real electrical power is written on its nameplate.
The meter at your front door doesn’t count watts, it counts energy: power × time. The unit is the kilowatt-hour, kWh (people often call it a "unit").
Change the hours in the table and see your monthly use. The price depends on your tariff band, so enter the price per kWh from your own bill.
Get at least 3 out of 4 right to tick off the lesson.
Values in the tables are approximate, for common household appliances. Always read the real power from the appliance’s nameplate. Your progress is saved on this device only.
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