How to accurately measure the Speed of Light

(in your own kitchen).

Equipment.

• The whites of 4 eggs.
• 1 large diner plate
• 1 ruler
• 1 Microwave oven

Procedure

1. Remove the glass turntable from the microwave oven.

2. Put the plate upside down on the floor of the oven so it covers the rotation mechanism.

3. Spread the egg whites evenly over the glass turntable.

4. Put the turntable on top of the upside down plate.

5. Turn the microwave oven on.

6. As soon as you see white patches appearing in the egg whites, turn the microwave oven off.

7. measure the distance between the centres of two adjacent white patches.

Calculation

The white patches show the maxima and minima of the electromagnetic sine wave generated by the magnetron in the microwave.

The distance measured is half of one wavelength. It should be a smidge over 6cm (about 61mm)

Therefore, the wavelength is about 12.2cm (122mm). or 0.122 Metres.

Now look at the label on the back of the Microwave oven to find out the frequency of the Magnetron. This should be about 2.45GHz,

The frequency is the number of oscillations per second (2,450,000,000 Hz)

In one second 2.45 billion waves will be produced.

If we know how long a single wave is, and how many are produced per second, we can calculate the distance the wave will travel in one second.

If you multiply 2.45 billion by 0.122 Metres you get 298,900,000 m/S

The actual speed of light is 299,792,458 m/s

Our measurement was accurate to about 0.3%

Conclusion

We just measured the Speed of Light, accurate to 0.3% with a ruler.