# Natural Science - Year II

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# Unit 52 Laboratory Activity: Microwave measurements

## Goal: To determine the length of an electromagnetic wave

This lab is based on Dave Ansell's Measuring the speed of light experiment.

### Materials:

• Easily meltable food (bar chocolate, chocolate chips, butter, or marshmallows)
• Flat tray that can be used in a microwave
• Centimeter Ruler

### Procedure:

1. Spread the food evenly on the tray.
2. Remove the "carousel" or other rotation device from the microwave.
3. Set the tray with the food on the floor of the microwave.
4. Run the microwave for 10-30 seconds, until melting spots appear on different places on the food. Do not melt the food entirely.
5. Measure the distance between melting spots. This distance is the distance between "troughs" of the wave and is equal to 1/2 the total wavelength.
6. Check the specifications for your microwave. These should list the frequency of the wave (usually around 100Hz).

### Report

1. Describe your setup and procedure.
2. Convert your measurements to meters (1cm = 1/100 meter).
3. Determine the average wavelength from your measurements. First, determine the average distance between spots, then multiply this distance by 2.
4. Calculate the speed of light as c = λ * ν where λ is the wavelength you measured and ν is the frequency of your microwave.
5. The actual speed of light is around 2.99 * 108meters/second. How accurate was your measurement?