Calculating the Speed of Light with a Bar of Chocolate
Objective
 To measure the wavelength of microwaves in a microwave oven.
 To record the frequency of the microwave oven.
 To estimate the speed of light.
Materials
Microwave oven, large block of plain chocolate, ruler and calculator.
Problem
The electromagnetic spectrum consists of high energy radiation such as gamma rays on the far
left of the diagram down to low energy radiation such as radio waves.
Gamma rays are extremely dangerous due their short wavelengths and high frequencies whereas
radio waves pose no threat due to their long wavelength and short frequencies.
All of the above types of radiation travel at the speed of light which is 300,000 km/sec.
or 3 × 108 metres/second.
For any form of radiation, the product of its frequency and wavelength in metres will always equal
the speed of light. This is one of the fundamental laws of the universe.
frequency  wavelength (in metres) = 300,000,000 m/sec
(f )

()
=
(c)
1
Note: 1nm (nanometer) = 1 × 10-9 metres
Using the equation: c = λ × f to complete the table below.
Types of Radiation
Frequency (Hz)
Wavelength (m)
X-rays
10-10
Visible light
3 × 1016
Gamma-rays
3 × 1025
Radio waves
2
Violet visiblelight
4 × 10-7
Red visible light
4 × 1014
Infrared light
1 × 10-5
Place the bar of chocolate in the microwave oven for 300 seconds, until the nodes appear.
First make sure the rotating plate is removed from the microwave oven. Record the distance between the
nodes which represents half the wavelength. Measure the distance between the nodes and record the results
in the table below. Repeat the procedure at least three times.
Complete the table below
Distance between nodes
(cm)
Wavelength ()
(metres)
Frequency (f)
Speed of light
metres/second
1st trial
2nd trial
3rd trial
Average =
2
3
Week
IT JUST KEEPS GOING! (MARCH 2, 2007)
Hi-res TIF image(2.5M)
This week SOHO observed sunspot 944 coming around the Sun's eastern limb--for the fifth time! Usually sunspots form
and dissolve in a matter of days or weeks, but this spot has real longevity-it has survived for an unusually long five
solar rotations. Here we put side-by-side images at almost exactly three of the five rotations. The Sun rotates about
once every 27 days.
A sunspot receives a new number each time it reappears, so three months ago this was called Sunspot 930 when it
blasted out a strong solar flare, one of the strongest in 25 years. Few months ago it was called Sunspot 923. Though
the numbers have changed, the spot remains true to its character: a source of magnetic intensity rising from beneath
the Sun's surface. Now, though, it is a mere shadow of its former self and poses no threat for such activity.
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