CPHY 122L
Lab 8
Measuring the Speed of Light with a Microwave Oven
1 Introduction
In Chapter 34 we will study electromagnetic waves. Light and microwaves are
familiar examples. In this lab exercise you will measure the speed of light
using a microwave oven by determining the wavelength of the microwaves
produced in the oven. The relationship between the wavelength and the
speed of light is
c=f; (1)
where fis the frequency.
The heating of foods by microwaves is caused by the transfer of energy
from the microwaves to the food. The key ingredient of food is water. The
energy transfer is made possible by the interaction of the water molecule’s
electric dipole moment with the microwaves. The potential energy of this
interaction is
U=pE;(2)
where p(p= 6:17 1030 Cm) is the dipole moment of a single water
molecule and Eis the time varying electric …eld of the microwave.
2 Purpose
Measure the speed of light.
3 Apparatus
Bar of Chocolate (or slice of cheese ): dimensions greater than 18 cm
8 cm.
Standard Consumer Microwave Oven
Paper Towel
Tooth Picks
1
