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How to Understand Electricity: Volts, Amps, Watts and Electrical Appliances

Eugene is a qualified control/instrumentation engineer Bsc (Eng) and has worked as a developer of electronics & software for SCADA systems.

A Beginner's Guide to Electricity

This guide for consumers and students explains all about volts, amps and watts and how they apply to home appliances and circuits. The equations are really quite simple, and you'll find some examples on how to apply them to home appliances.

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Electricity 101: Understanding the Basics

In this tutorial, you'll learn about:

  • volts, watts, amps
  • power consumption of appliances and kilowatt hours (kWh).
  • Ohm's law and resistance
  • resistivity and how it affects the resistance of a material
  • fuses and how they protect wiring and appliances
  • how electricity is produced
  • devices used to measure voltage, current and resistance
  • the effects of electric and magnetic fields
  • conductors, insulators and superconductors
  • the basics of AC and DC
  • arcs and sparks
  • power supplies and voltage regulation
  • tracking electricity usage in the home

What is Electricity and an Electric Current?

An electric current is a flow of electrons in a conductor. All matter is made from basic building blocks called atoms. A simplistic model of an atom, known as the Rutherford–Bohr model or Bohr model or Bohr diagram has a central nucleus made up of particles called protons and neutrons. The nucleus is surrounded by orbitals containing electrons. In some materials such as metals, electrons are bound loosely to the nucleus so they can detach and move when a voltage is applied. These materials are known as conductors and can conduct electricity. The flow of electrons is called a current.

Conceptual image of atom with protons and neutrons in the central nucleus and electrons in outer orbitals

Conceptual image of atom with protons and neutrons in the central nucleus and electrons in outer orbitals

Electrons with a negative charge flowing through a conductor

Electrons with a negative charge flowing through a conductor

In reality, electrons don't actually move from one end of a conductor to another. Instead they transfer energy between each other just like the steel balls in this Newton's cradle, while moving negligibly themselves.

In reality, electrons don't actually move from one end of a conductor to another. Instead they transfer energy between each other just like the steel balls in this Newton's cradle, while moving negligibly themselves.

How Does Current Flow in a Circuit?

In the photo below, an AA cell, which is an example of a voltage source, powers a torch bulb. Electric current first flows out the top of the battery, through the wire and bulb and then returns via the bottom wire. So it always flows in a loop and two wires are needed to connect the voltage source to the load.

In this example of a simple circuit, an AA cell forces current through the wires and lights up a bulb

In this example of a simple circuit, an AA cell forces current through the wires and lights up a bulb

We can represent this circuit in a simple manner using a schematic or circuit diagram. Looking at the schematic below, a voltage source V will force a current I around the circuit through the load (the bulb in this case) whose resistance is R.
The load R could be an electrical appliance such as a heater, bulb, LED, motor or component in an electronic circuit. The lines joining the source to the resistance would be the connecting wires inside an appliance or power flex, or tracks on a printed circuit board.

Ohm's Law
The current I measured in amps is given by the equation:

I = V/R

We'll cover Ohm's Law in more detail later and see some examples

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A schematic of of a simple circuit. The voltage source V causes current I to flow around in a loop through the resistance or load R.

A schematic of of a simple circuit. The voltage source V causes current I to flow around in a loop through the resistance or load R.

Voltage (measured in volts) forces current (measured in amps) through the resistance of a circuit (measured in ohms).

Voltage (measured in volts) forces current (measured in amps) through the resistance of a circuit (measured in ohms).

Current Direction in a Circuit

Conventionally we think of current flowing out the positive terminal of a source such as a battery. However current is a flow of sub-atomic particles called electrons which are negatively charged, so current actually flows the other way, from the negative terminal of the battery.

What are Examples of Voltage Sources?

  • Battery
  • Mains voltage at a socket outlet
  • Alternator or DC generator (dynamo)
  • Solar cell
  • Thermopile
  • Laboratory power supply

The Water Pipe Analogy for Explaining Electricity

Voltage and current are like water pressure and water flow rate respectively, and reference is often made to pumps and water pipes as an analogy to explain electrical circuitry.

What's the Difference Between Watts, Amps and Volts?

Like any discipline, electrical engineering has jargon or specialized terminology.

  • What Are Volts?

    Voltage is the pressure in a circuit and measured in volts. Think of a pump in a water pipe. The greater the pressure and the force which the pump exerts, the greater will be the flow of water through the pipe. Similarly a voltage source is like a pump and pushes electrons around the circuit. The higher the voltage applied to a circuit, the greater the current which will be forced through it.

  • What Are Amps?

    An electric current is due to the movement of electrons through a conductor and load and is measured in amps. High current means lots of electrons flowing through the circuit. The water analogy is water flow rate in gallons per minute.

  • What is a Load?

    This is the device connected to a voltage source. It could be a motor, bulb, heater, LED, or an electronic resistor.

  • What Are Watts?

    Power is the rate at which energy is consumed by a load and is measured in watts. A kilowatt is 1000 watts, also abbreviated to kW. Low powers are measured in milliwatts (mW) or thousandths of an amp.

  • What Are KWh or Kilowatt Hours?

    Kwh are a measure of energy consumption. KWh are sometimes called units and are what you pay for on your electricity bill. A 1 kilowatt (1000 watt) appliance uses a kilowatt hour of electricity in one hour. Similarly a 500 watt device uses a kilowatt hour of electricity in 2 hours.

What Are Some Commonly Used Voltages ?

Commonly used voltages of devices and systems.

Voltage SourceVoltage

AA or AAA cell

1.5 volts

Mains supply in the home

Nominally 120 or 240 volts

Car battery

12 volts

Truck battery

24 volts

Voltage input to transformer supplying home

Greater than 10 kV (kilo volts)

High voltage transmission lines

Up to 1.2 MV (Mega volts)

How to Convert Between Volts, Amps and Watts

Now let's examine the quantities which are usually of interest when dealing with appliances, such as volts, amps and watts and how to convert between them. If you look at the casing of an appliance (see photo below) you can usually find a specification label or panel which indicates the voltage supply, frequency, wattage and possibly current. On some appliances e.g. TVs and washing machines, this panel may be mounted at the back of the device.
This is the equation we need to remember. Once we know it, we can rearrange to find the other two.

watts-amps-kilowatt-hours-what-does-it-all-mean

Examples of Working Out Watts, Amps and Volts For Appliances