ELECTRIC POP-UP TOASTERModern toasters are typically one of three varieties: Pop-up toaster, Toaster oven and Conveyor toaster Pop-up toaster Toaster oven Conveyor toasterFor home use consumers prefer a pop-up toaster. For lots of people the toaster is a daily part of breakfast as it is an easy to use appliance. All a person needs to do is insert bread slices into the slots, select the degree of toasting by turning the Heat level adjustment knob to desired level and then push down the lever to start the process of toasting. When an internal device determines that the toasting cycle is complete, the toaster will turn off and the toast 'pops' up, out of the slots. The toaster may seem like a simple device to use, but some questions do pop up like:How exactly does the toaster toast the bread?

How does the toaster know when to pop the toasted bread up?

In this article we'll study the toaster closely so that we can answer the above questions. To begin with let us first define a toaster, "A Toaster is designed to heat the sides of a slice of bread for the right amount of time turning the slice of bread into toast ". Now lets understand the parts of a toaster which work together to make a perfect toast. As shown in the figure below a toaster mainly consists of: Figure 1 Figure 2Top slots: These are the openings on the top of the toaster to insert the slices of bread.

Push down handle / Lever: This lever when pushed down initiates the process of toasting.

Heat level adjustment knob: This helps set the toasting time.

Heating elements: These are coils of wire inside the toaster made of copper or nichrome.

Cage: This is where the bread slices rest inside the toaster while toasting.

Power Cord: This supplies electrical current to heat the heating elements.

Lets understand how the toaster toasts a bread. A toaster is an electrical appliance, hence it requires electricity to operate. When electric current flows through the heating elements inside the toaster, the electrical energy is transformed into heat which means that these coils of wire called heating elements become very hot. They heat up everything around them, including the bread. When the bread is close to the heating element for the right amount of time, it turns a light brown color and transforms to a toast. If heated for too long the toast will turn black and begin to smoke. Toasters are generally built so that they stop on their own to prevent this from happening. Heating of the coils a perfect light brown toast Effects of overheating, burnt toast This takes us to the question of how does the toaster know when to stop. A pop up toaster causes the toast to 'pop-up' when it stops. When the bread is first inserted through the slots, the cage inside the toaster holds it up slightly out of the slots. At first the heating elements are not hot because no electrical current is flowing through them. When the lever is pushed down, the bread slices are lowered all the way in and this brings the breads very close to the heating elements. There are two important things that happen when the lever is pushed down:1.The toaster allows the electricity to flow through the heating elements which starts the process of toasting the bread.

2.A spring is compressed inside the toaster and a latch holds the lever in place at the bottom position. Even if the lever is released at this point, the latch will keep it in place and the bread will continue to toast.

Now along with the heating elements there is one more part being heated within the toaster, it is called the Release-mechanism. This part is designed to change its shape as the temperature increases. Eventually the Release-mechanism heats up enough that the latch is released and this is what makes the popping sound. Once the latch is released the spring quickly pulls up on the lever. This stops the flow of electric current and allows the heating element to begin cooling down. Simultaneously the spring also pulls up the cage through the slots, so that it is easy to remove the toasted bread slices. The time on the release mechanism is determined by the Heat Level adjustment knob settings, which will cause the bread to toast lighter or darker.We have had an exciting journey of understanding how a simple bread slice transforms to a yummy toast. So, next time you when you use a toaster proudly say "I know how that works".

Compiled by: Sowmya KapadiaDate: 20th Sept 2014 Completion time required: 6 hours