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Typical electric toaster

Electric toasters

by Chris Woodford. Last updated: November 7, 2013.

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: An electric toaster takes in electrical energy from the power outlet and converts it into heat, very efficiently. If you want your toast to cook quickly, you need a toaster that radiates as much heat as possible each second onto your bread. For that to happen, according to the laws of physics, it needs to consume the maximum amount of electrical energy per second. In other words, it needs the highest power rating (wattage) you can find. A toaster with a higher watt rating will invariably cook more quickly than one with a lower rating.

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?

Illustration showing electrons flowing round a circuit between a battery and a lamp

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.

What happens inside a toaster?

Illustration showing how a toaster turns electricity into heat

  1. Electrical energy flows into the toaster from a wire plugged into the domestic electricity supply.
  2. The electric current flows through a series of thin filaments connected together but spaced widely enough apart to toast the whole bread surface.
  3. The filaments are so thin that they glow red hot when the electricity flows through them.
  4. Like a series of small radiators, the filaments beam heat toward the bread in the toaster.
  5. The steady supply of heat rapidly cooks the bread. There are filaments on each wall of the toaster so the two sides of the bread cook at the same time.

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 light for more details of how atoms produce light.)

Old-fashioned electric lamps use this trick to produce their 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.

Elements glowing red hot inside a toaster Element inside electric kettle

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?

Your toaster most likely uses either a timer or a thermostat to switch itself off when your bread is done.

Timers

It's reasonable to assume that most people always use the same kind of bread, sliced in a similar way, so their toast will usually take about the same length of time to cook. A simple clockwork or electronic timing circuit can be used to switch off the heating element after a certain period has elapsed. With this kind of toaster, turning up the control simply extends the cooking time.

Thermostats

A thermostat is a mechanical, electrical, or electronic device that switches an electric circuit on or off to keep something (perhaps the room where you're living or the ice compartment of a refrigerator) at a fairly constant temperature. We can also use it to switch a toaster off when the bread is cooked. Suppose there is a bimetal-strip thermostat (two different metals welded together) fitted very close to a toaster's heating element. The thermostat will heat up as the bread cooks and the metals will expand by different amounts, so the thermostat will gradually bend into a curve. When the right temperature is reached, it will bend just enough to snap open and switch off the toaster's heating element. In this kind of toaster, turning up the control adjusts the distance by which the thermostat has to bend before it switches off the heater.

Pop-up!

When timers and thermostats switch off a toaster, they generally also release a spring that pops up the metal cage holding your toast. It's much 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—and, as we've seen already, you don't want to touch the filaments!

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Text copyright © Chris Woodford 2007. All rights reserved. Full copyright notice and terms of use.

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Woodford, Chris. (2007) Electric toasters. Retrieved from http://www.explainthatstuff.com/electrictoasters.html. [Accessed (Insert date here)]

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