Name______Date:______

Measuring the Speed of Light Using a Microwave (614)

Take Home Lab

Materials:

  • construction paper
  • fruit roll-ups
  • Metric ruler
  • Microwave oven

Procedure:

  1. Evenly spread the fruit roll-ups on the bottom of the construction paper.
  2. Turn the turntable off or remove the turntable from the microwave so the paper will not rotate.
  3. Place the sheet of fruit roll-ups in the microwave and microwave on high until about five hot spots develop. The fruit roll-up will bubble and darken at the hot spots.
  4. Remove the construction paper carefully!
  5. Use the ruler to measure the distance between the dark melted spots (this is the distance between the antinodes of the microwaves) in the fruit roll-ups. Record your data.
  6. Look at the tag on the back of the microwave for the frequency of the microwave and record this number as well (or do some research and find out the frequency of the microwave you are using).

Data:

Distance between antinodes (cm)
Measurement #1
Measurement #2
Measurement #3
Measurement #4

Frequency: ______Hertz

Data Analysis

1. Average the distance between the antinodes. Show your work below.

2. The distance between two antinodes is only 1⁄2 a wavelength. Therefore, you must multiply the average distance by 2 to get the wavelength. Show your work.

3. Convert your wavelength to meters. Show your work.

4. Calculate the speed of light.

Knowns:Calculations/Solution:

Explanation

Microwaves are a type of electromagnetic wave with a wavelength of about 0.01 cm to 1 meter. Microwave ovens work by setting up standing waves inside the oven that twist the water molecules in the food back and forth until they heat up. Most microwave ovens have a wavelength of about 12 cm. In the picture of the standing wave to the right you can see the nodes and antinodes of a wave in a microwave oven. The highest energy of the wave occurs at the antinodes of the wave. This is where the hot spots in a microwave oven occur. Most microwaves have a turn-table because the food needs to be rotated to place most of the food in the path of the hot spots. A hot spot occurs ever 1⁄2 a wavelength or approximately 6 cm.

Questions:Write complete answers using complete sentences.
  1. What problems could arise (due to the phenomena examined today) when cooking food in a microwave oven?
  1. Explain two ways of overcoming these problems.
  1. Astronomers will tell you that when you are looking at stars you are looking into the past. Is this true? Explain what is meant by this statement.