Lab 4: Measuring the Speed of Light with Chocolate

Measuring the Speed of Light With Chocolate (15 points, 20 if you vlog the activity)


Total Duration:
20 minutes
Materials and Equipment:
1. Microwave
2. Chocolate chips or a big bar of chocolate--the cooking size.
3. Paper plate
4. Ruler

Procedures:
Remove turntable from microwave
Scatter a single layer of chocolate chips over paper plate, or use a big bar of chocolate.
Place in microwave
Microwave for a few seconds (depends on microwave--15 to 45 seconds) until chocolate starts to melt
Measure the distance between hotspots



Measuring the Speed of Light with Chocolate
(adapted from apps.caes.uga.edu/sbof/main/lessonPlan/MeasuringSpeedLightChocolate.pdf )

Anyone can measure the speed of light (c) - with chocolate and a microwave
oven! The only equipment you need for this experiment is a microwave, a ruler
and chocolate.

The speed of light is equal to the wavelength (λ) multiplied by the frequency (f)
of an electromagnetic wave (microwaves and visible light are both examples of
electromagnetic waves).

c=λ*f

When you turn on your microwave oven, electrical circuits inside start generating
microwaves – electromagnetic waves with frequencies around 2.5 gigahertz –
2500000000 Hz. These waves bounce back and forth between the walls of the
oven. The size of the oven is chosen so that the peaks and troughs of the
reflected waves line up with the incoming waves and form a “standing wave”.
The electromagnetic field inside the microwave behaves in roughly the same way
as a guitar string except the vibrations are in “the electromagnetic field”. Where
the vibrations are greatest (the antinodes), you will see the greatest heating, but
at the nodes, the chocolate will only melt slowly as heat diffuses into those
areas.


You do it.
Remove the turntable from the microwave (so the plate does not rotate). Place
chocolate scattered on a plate inside the microwave. Heat the chocolate until it
just starts to melt - about 20 seconds. There will be some melted hot spots and
some cold spots in the chocolate.
The distance between the melted areas is half the wavelength of the microwaves
or the distance between the antinodes. So, from this simple experiment, and
some easy math, you can work out the speed of light!
c=2*x*f
Distance between the hot spots ______________________________cm
Wavelength _____________________________________________cm
Wavelength _____________________________________________m
Frequency of the microwave ________________________________m
EQUATION _____________________________________________
Your calculated speed of light _______________________________m/s