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Festival Of Science


Calculating the speed of light in your kitchen
Doctor Chris prepares to experiment

BBC Look East at the speed of light

Take part in the BBC Look East experiment to calculate the speed of light in your kitchen using a plate of bread and margarine and the help of Chris Smith from the Naked Scientists.

BBC Look East is looking for the region's kitchen sink scientists to measure the speed of light with just a microwave, some bread, margarine and a ruler.

If you are under 16 years of age, please ask an adult to help you with this experiment.

Watch video Watch: Experiment to calculate the speed of light in your kitchen
Audio and Video links on this page require Realplayer

You will need:

A microwave oven
A microwave-proof plate
A bowl (to cover microwave turntable mechanism)
An oven glove or tea-towel
A ruler

Four slices of bread
A tub of margarine

The experiment

First of all, arrange four slices of bread on a plate - putting them as close together as you can. Imagine you've created one giant slice of bread from the four slices.

Chris with his microwave
Chris with his microwave

Now spread the slices with really, really thick margarine - making sure to spread over the joins between the slices. When finished it will look like one giant slab of margarine.

Into the microwave oven

Take the turntable out of the microwave and cover the turning mechanism with a shallow bowl or plate.

Microwaves create waves that have hot and cold spots.

Normally the turntable is there to get rid of those spots to ensure an even cooking process, but for this experiment we want to use those hot and cold areas.

Once you've taken out the turntable and covered the mechanism, place your plate of bread and margarine in the microwave and cook it for a maximum of 20 seconds.

You're looking for melted spots to start appearing in the margarine. As soon as this starts to happen, turn off the microwave.

Using the oven glove (or tea towel) to protect your fingers from any heat coming off the plate, carefully take out it out of the microwave and place it on the kitchen worktop or table (making sure it's a suitable place to put a slightly warm plate).

Hot-spots are the clue

The margarine should have some melted spots in it as the microwave creates a series of energy waves which run back and forth across the oven and its contents.

Where the wave is at a peak or trough, these are the hottest spots, or where the energy is at its greatest.

At these points, the food is cooked - or in this case it's the spots where the margarine has melted.

This is created by a single wavelength.

Scientific data

Speed of light Calculator

Just type in the distance between the melted bits of margarine, and the frequency off the back of your microwave (sometimes it's inside the door) to calculate the speed of light in your kitchen.

Distance between melted margarine
Frequency on back of microwave

This will send your data to the Naked Scientists website. This is an external website not part of the BBC
The BBC is not responsible for the content of external internet sites

If we now measure the horizontal distance between two melted areas (it can be on the bottom or top of the slice of bread) this is half a wavelength.

Remember this measurement, it's what you'll need to allow our computer to calculate the speed of light.

Next you need a number from the sticker on the back of your microwave.

You are looking for the frequency - either in mega or gigahertz - which is the number of waves your microwave makes every second. Do not confuse this with the power rating, which is measured in Watts (650W, 750W, 850W).

Doing the sums

To calculate the speed of light multiply how big the waves are (the measurement you've just taken between the melted areas) by how many waves there are per second (the frequency number from the back of your microwave).

Put these numbers into this calculator (selecting the unit of measurement you've used and the frequency output of your microwave) and press convert.

Now you have how fast the speed of light is according to your kitchen.

Once the calculator has given you a figure, you can continue to submit your findings to The Naked Scientist website to be included in their Hall Of Fame.

How close is your measurement to the speed of light? Find out by visiting The Naked Scientists' website. Where you can also see how other people got on with this experiment.
The BBC is not responsible for the content of external websites

If you're wondering what to do with the bread, here are some recipe ideas from BBC Food.

 



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