Lab report

Experiment 2: Wave Speed of Microwaves

When you cook food in a microwave, it is heated by an energy transfer in the form of microwaves. When the microwaves encounter the wall of the oven they bounce back and create standing waves which in turn create nodes and antinodes. Antinodes and nodes are manifested in the form of hot spots (to avoid uneven cooking most microwaves include a turntable) and are equal to one half of the microwave's wave length. In this experiment, you will determine the speed of microwaves and observe the effects of wave reflection using marshmallows.

Materials Paper Plate Ruler *6 Large Marshmallows *Microwave with Labeled Frequency	*You Must Provide *Do Not Consume

Procedure

1. Use a microwave that has a labeled frequency. Most microwaves have a frequency of 2450 MHz. Note: Most microwave frequencies can be found on a sticker inside or on the back of the microwave.

2. If the microwave has a turntable, either turn the turntable off or remove it for the experiment.

3. Place a straight line of six marshmallows on the paper plate so that they are touching end to end.

4. Place the plate with marshmallows in the microwave.

5. Allow the marshmallows to cook until you see some of them start melting. As soon as they start melting, stop cooking the marshmallows. Note: The marshmallows will start melting within thirty seconds. LAB SAEFTY: To avoid burns allow marshmallows to cool before handling them.

6. Measure the distance across a melted hot spot. Record your answer in Post-Lab Question 1.

Post-Lab Questions

1. What is the distance in centimeters of a melted marshmallow hot spot? In meters?

2. Based on your measurement of the hot spot what is the wavelength of a microwave?

3. Calculate the wave speed of microwaves from the labeled frequency and your measured distance?

4. Is this speed close to the speed of light? Explain why or why not.

5. Why was it important to remove the turntable function? How might the results vary if the turn table was functional during the experiment?