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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:
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.
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| 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
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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.
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
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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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