Electric toasters

Last updated: September 18, 2007.

Yum, what could be better than a nice crisp piece of buttered toast first thing in the morning? If you don't like standing by the stove watching and waiting for your bread to turn brown, an electric toaster could be just the thing for you. You probably know that a machine like this turns the power of electricity into heat that can cook your bread in a jiffy. But you do you know how the electricity that flows into the toaster gets transformed into a totally different kind of energy? Let's take a closer look inside.

Photo: A typical electric toaster.

Turning electricity into heat

Energy is a kind of magic, invisible substance that lets you do things. Heat is one kind of energy and electricity (generated by power plants and stored inside things like batteries) is another. You can't make toast by standing a slice of bread on top of a battery—and nor should you try! But you can make toast with electricity if you use an electric toaster. So what's the difference?

If you've ever looked down inside a toaster, you'll have noticed rows of glowing red wires facing the bread. When electricity flows through these wires, they get hot and then fire their heat toward the bread like dozens of miniature radiators.

WARNING: You must never ever touch these wires (which are called filaments or elements), either with your fingers or with any other object, because they are dangerously hot and carry large electric currents that could zap through your body, electrocute you, and kill you. If you need to remove some bread stuck in a toaster, always unplug it first.

When electricity flows through a wire, energy is transmitted from one end of the wire to another. The movement of energy is a bit like water flowing down a pipe. The electrical energy is carried down the wire by electrons, the tiny particles inside the atoms of metal that make up the wire. As the electricity flows, the electrons jostle about and collide with one another, and with the atoms in the metal wire, giving off heat in the process. The thinner the wire, and the greater the electric current, the more collisions happen and the more heat is generated.

Heat and light

Heat is not the only thing that's produced when electricity flows down a wire. If the wire is thin enough, and providing it's not covered with plastic insulation, its temperature may rise so much that it glows red hot. What's happening here? If the wire is glowing, it must be giving off light. The atoms inside the metal wire are being heated up by the electrons flowing through it. They're absorbing some energy as heat, becoming unstable, and then giving off some of the energy as light to try to become stable again. (See our article on fluorescent lamps for more details of how atoms produce light.)

Photo: Yum, toast!

Old-fashioned electric lamps use this trick to produce light. Inside their large glass bulbs, they have a filament made from an incredibly thin piece of coiled wire. When electricity flows through the filament, it becomes extremely hot and produces both light and heat. Making light by heating something up in this way is called indandescence. Incandescent lamps waste most of the electrical energy they consume. About 90 percent of the electricity in a light bulb like this turns immediately into heat, which is incredibly wasteful. That's why many people are now switching over to energy-efficient fluorescent lightbulbs, which produce just as much light without producing heat.

In a toaster, the opposite is the case: we're obviously much more interested in producing heat and the small amount of light produced by the glowing filaments is wasted energy.

It's elementary

Toasters and incandescent electric lights are just two examples of many household appliances that make heat when electricity flows through them. Electric showers, coffee machines, radiators, fan heaters, hair dryers, hair curlers, irons, tumble dryers, washing machines, and cookers work in a very similar way. (Microwave ovens, however, work in a completely different way, using electromagnetic radiation to zap heat into water molecules inside your food.)

Appliances such as showers and kettles that heat up water with electricity have to do it in a safe way to ensure they don't electrocute you. Instead of using a thin bare wire (like the ones you can see inside your toaster), they use a different kind of heating unit called an element, which has the bare wires safely contained inside it. The element is the shiny curved piece of metal you can see at the bottom of an electric kettle. Don't ever attempt to touch it because you'll burn or otherwise injure yourself.

Photo: Left: The glowing elements inside a toaster. Right: You can clearly see the coiled electrical element at the bottom of this kettle. As electricity flows through the thick metal coil, electrons inside make the metal heat up and that heat is rapidly passed onto the water inside the jug.

How do toasters know when to switch themselves off?

Most toasters have electrical or mechanical devices on them that switch off the electricity after a certain time has elapsed. So if you set the toaster to cook your bread more, you're actually just leaving it on for longer. When the timer switches off, it activates an electric switch that releases a spring and pops up your toast. It's easier to get your toast out if it pops up. It's safer too because the inside of the toaster is usually much too hot to be reaching into.