Speed of Light

Once as the Queen of Science, Lizzy started a fire in her school. The students had to be evacuated. The fire department showed up, and they weren’t very happy to find it was a false alarm. The principal said, “We’ve been doing science in this building for years and no one has ever started a fire.” Lizzy said, “Then, they weren’t doing it right.”

“Your kids and grandkids will be impressed by your knowledge of physics”

It was a fun experience, that the students loved… and it can be performed safely at home with a simple precaution, but I’ll get to that later. 

The Physics

The experiment… use a microwave oven to calculate the speed of light. So that your child understands the physics, you’ll need to explain how a microwave oven works. 

A microwave is a form of electromagnetic radiation, just like light, but it is beyond the visible spectrum so we cannot see this type of light. A microwave oven works by creating a oscillating wave in the oven. One wavelength is kinda like a jump rope being shaken up and down. The frequency is the rate at which the oscillations of the jump rope occur. 

This oscillating wave moves through the food. The peaks of the wave heat faster, which is why food heats unevenly, and why most microwave ovens have a tray to spin the food. What you will measure is a half wavelength, from one peak to another. You multiple this times two for a full wavelength of the microwave light.

Materials

• Microwave oven
• Microwave safe dish 
• Two Chocolate bars
• Ruler
• Calculator

Steps

1. Place two chocolate bars side-by-side on the microwave safe dish.
2. If your oven has a rotating tray, remove it. We don’t want the dish to rotate.
3. Put the dish in the oven for 10 seconds. The microwaves will hit the food over and over again at the same spots.
4. When you remove the dish, you’ll notice melted pools on the chocolate bars. (Time may depend on the microwave – if all or none of your chocolate melts, adjust the time a few seconds.)
5. Measure the distance between melted pools using a ruler. Measure in centimeters. This measurement is half the wavelength of a microwave.
6. Look for a sticker on your oven that tells you its frequency in Hertz (Hz). Hertz is a measure of  the number of cycles per second. Most microwave ovens are around 2450 MHz. (2,450,000,000 Hertz) 
7. Use the following equation to calculate the speed of light: 2 x (distance between melted spots) x (frequency of microwave)

The actual speed of light is 29,400,000,000 centimeters per second. How close were you?

A Simple Precaution

Use a microwave safe dish! Lizzy used paper plates. She performed this experience multiple times each day, for multiple groups of students. To avoid washing dishes, she used paper plates. We agreed ahead of time that this would be fine, as long as she did not let the microwave run longer than 10 seconds. More time than that and the paper would likely catch fire. She did and it did. So, to avoid calling the fire department, use a microwave safe dish and only run your oven for 10 seconds. Your kids and grandkids will be impressed by your knowledge of physics, and learn that Science Can Be Fun fun.

“And God said, ‘Let there be light,’ and there was light.” 

Genesis 1:3

Copyright © 2023 Chuck Locklear