Measuring the Speed of 'Light' with a Microwave Oven | Science Project (2022)

Science Projects

Abstract

Did you know that you can measure the speed of light using a microwave oven, some egg white, and a ruler? Find out how with this cool kitchen science project thanks to Mr. Nick Hood, a science teacher in Fife, Scotland.

Summary

Areas of Science

Physics

Difficulty

Time Required

Very Short (≤ 1 day)

Prerequisites

You'll need a microwave oven to do this project. You'll get the most out of this project if you've taken (or are currently taking) a course in high school physics.

Material Availability

Readily available

Cost

Very Low (under $20)

Safety

Adult supervision recommended

Credits

Andrew Olson, PhD, Science Buddies

Sources

The idea for this project and the microwave oven images are from:

  • Hood, N. (2007). Measuring the Speed of Light in the Kitchen.

We believe the idea behind this science project can be first traced back to this publication:

  • Stauffer, R.H., Jr. (1997, April). Finding the Speed of Light with Marshmallows - A Take-Home Lab. The Physics Teacher, 35, 231.
(Video) How do you measure the speed of light using a microwave oven?

Measuring the Speed of 'Light' with a Microwave Oven | Science Project (1)

Objective

The goal of this project is to measure the speed of electromagnetic waves in the microwave portion of the spectrum by measuring the spacing between hot spots in a microwave oven.

Introduction

Microwaves, like light, are an example of electromagnetic waves. Electromagnetic waves can travel through the vacuum of interstellar space. They do not depend on an external medium-unlike a mechanical wave such as a sound wave which must travel through air, water, or some solid medium. Electromagnetic waves cover a huge range of frequencies, from high-frequency gamma rays and x-rays, to ultraviolet light, visible light, and infrared light, and on into microwaves and radio waves. As the frequency decreases, so does the energy. The wavelength of an electromagnetic wave is inversely proportional to its frequency. So waves with high frequency have short wavelengths, and waves with low frequency have long wavelengths.

Electromagnetic waves interact with materials in different ways, depending on the nature of the material and the frequency of the electromagnetic wave. Microwaves work well for cooking because their energy can be efficiently absorbed by molecules commonly found in food, including water, sugars, and fats. The absorbed microwave energy heats these molecules and cooks the food. As you can see in Figure 1 below, the range of microwave wavelengths is from 0.01 cm to 10 cm.

Measuring the Speed of 'Light' with a Microwave Oven | Science Project (2)

The electromagnetic spectrum extends from very short wavelength gamma rays to very long wavelength radio waves. The focus of this diagram is to display the portion of the spectrum that is visible to the human eye. Wavelengths between 400 and 700 nanometer are visible as colors and make up a very small portion of the electromagnetic spectrum.


Figure 1. The electromagnetic spectrum. Electromagnetic radiation covers a huge range of wavelengths. Light (the part of the electromagnetic spectrum that we can detect with our eyes) is only a small portion of this range. X-rays, light, and microwaves are all examples of electromagnetic waves. (Illustration from Abrisa Glass & Coatings, 2005)

In this project you will take advantage of some physical properties of waves in order to estimate the speed of light. These properties are interference and the relationship between a wave's speed, its frequency, and its wavelength. Interference is what happens when multiple waves interact. For example, at the beach, the incoming waves from the ocean and the outgoing waves from the surf drawing back from the beach interfere with one another. When two wave crests coincide, they combine to make an even higher crest. When two wave troughs coincide, they combine to make an even lower trough. When a wave crest and a wave trough coincide, they tend to cancel each other out. Interference is the name physicists use for this kind of combination of waves.

In a microwave oven, interference occurs between waves that are reflected from the inside surfaces of the oven. The interference patterns can create "hot" and "cold" spots in the oven-areas where the microwave energy is higher or lower than average. This is why many microwave ovens have rotating platters to promote more even cooking of the food. In the experiment described below, you'll remove the rotating platter (if your oven has one) in order to see the effects of the interference pattern on your cooking. You'll cook an egg white just long enough for some parts of the egg to solidify, while the rest remains partially cooked. The egg white will cook fastest at the hot spots in the oven. The distance between the hot spots will be equal to half of the wavelength of the microwaves. You will be able to measure the distance between the hot spots by measuring the distance between the cooked portions of the egg.

So measurements from your cooking will give you the wavelength of the microwaves. With one more piece of information, the frequency of the waves, you will be able to calculate the speed of light. You should be able to find the frequency of the microwaves on a label on the back of the oven. The frequency (f), wavelength (λ, and wave speed (v) are related by the equation: v = f λ.

The Experimental Procedure section has all the details for doing the experiment. Do your background research and then go cook some eggs and see what they can tell you about the speed of light.

Terms and Concepts

To do this project, you should do research that enables you to understand the following terms and concepts:

  • Waves
    • Frequency
    • Wavelength
    • Speed
    • Standing waves
    • Interference
  • Electromagnetic spectrum
  • Microwaves
  • Microwave oven
  • Magnetron

Questions

  • What is the relationship between wave speed, frequency, and wavelength?

Bibliography

  • For more information on the physics of microwave ovens, see:
    Baguley, R and McDonald, C. (Dec 1,2014). Appliance Science: The tasty physics of microwave ovens. Retrieved April 12, 2018.
  • For more background information on waves, standing waves, and interference, see the following:
    The Physics Classroom. (n.d.). Waves. Retrieved May 5, 2014.

Materials and Equipment

To do this experiment you will need the following materials and equipment:

  • Microwave oven
  • Plate (safe for use in microwave)
  • Oven mitts
  • 3-6 eggs
  • Ruler
  • Calculator

Experimental Procedure

Safety Note: The materials used in the microwave oven will get hot! Use oven mitts, and be careful so you don't get burned!

  1. Do your background research so that you are familiar with the terms, concepts, and questions in the Background section.
  2. If your oven has a rotating platter, remove it. You won't be able to detect "hot spots" in the oven if your test plate is moving.
    1. Tip: you may not be able to remove the drive mechanism for the turntable in your oven. In that case, you can make a support for your egg plate by placing a flat-bottomed, microwave-safe bowl upside down over the drive mechanism. Naturally, the bowl needs to be large enough so that the drive mechanism does not touch it. It also needs to provide sturdy support for the plate used for cooking the eggs.

Measuring the Speed of 'Light' with a Microwave Oven | Science Project (3)
Figure 2. A microwave oven with the rotating platter removed and drive mechanism removed. If the drive mechanism on your oven does not come out easily, follow the instructions above. (Hood, 2007)

(Video) How To Calculate The Speed Of Light With Your Microwave

  1. Crack an egg and separate out the egg white (allow the white to drain into a bowl, and hold the yolk back in one half of the broken shell).
  2. Pour some of the egg white onto a microwave-safe plate.
    1. You should have puddles (or stripes) of egg white that are at least 12 cm in diameter (in length).
    2. To sample over the largest area possible, use a plate that is close to the inside dimensions of the microwave.
  3. Put the plate in the oven, close the oven door, and cook the egg.
    1. You'll probably need to experiment to find the ideal cooking time for your particular oven. 30 seconds may be a good starting point. If the egg is completely cooked, start over and decrease the time. If the egg is still totally uncooked, increase the time. If you don't disturb the plate, you can simply add more time. If the plate moves, you'll need to start over with a fresh plate of uncooked egg white.
    2. The ideal result is to have egg white that is partially cooked in some places, and nearly completely cooked in other.
  4. Use oven mitts to remove the plate from the oven. Be careful not to move the egg on the plate. Allow the plate to cool.
  5. Measure the spacing between the cooked portions of the egg. Notes:
    1. The centers of the cooked portions will not be clearly defined.
    2. Your goal in making this measurement is to find:
      1. the average distance between the cooked portions, and
      2. an estimate for the error of your measurement.

      Measuring the Speed of 'Light' with a Microwave Oven | Science Project (4)
      Figure 3. Using the cooked portions of the egg white to measure the distance between "hot spots" in the microwave oven. (Hood, 2007)


    3. Measuring the "center-to-center" distance between adjacent cooked portions will give you the average spacing of the hot spots.
    4. Measuring the "edge-to-edge" distances (both shortest and longest) between adjacent cooked portions will give you upper and lower bounds on the error of your measurement.
  6. Clean and dry the plate, and repeat the experiment at least three times.
  7. Look at the label on the back of the microwave to find the frequency of the microwave radiation the oven produces (see the illustration below). Alternatively, you may find this information in the user's manual for the oven.

    Measuring the Speed of 'Light' with a Microwave Oven | Science Project (5)
    Figure 4. Example of a microwave oven label, showing the frequency of the microwave radiation: 2450 MHz. (Hood, 2007)


  8. The spacing of the hot spots will be equal to one-half of the wavelength of the microwaves.
  9. Calculate the speed of the microwaves using the wavelength (measured) and frequency (from the oven label). Remember to use your upper and lower boundary measurements to put error limits on your measurement.
  10. How closely does your calculation agree with published values for the speed of light?

Measuring the Speed of 'Light' with a Microwave Oven | Science Project (6)

Ask an Expert

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Variations

  • The Science Buddies project Using a Laser to Measure the Speed of Light in Gelatin has another method for measuring the speed of light in your kitchen.
  • For another experiment on standing waves, see the Science Buddies project How to Make a Guitar Sing.

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MLA Style

Science Buddies Staff. "Measuring the Speed of 'Light' with a Microwave Oven." Science Buddies, 23 June 2020, https://www.sciencebuddies.org/science-fair-projects/project-ideas/Phys_p056/physics/measuring-the-speed-of-light-with-a-microwave-oven. Accessed 9 Oct. 2022.

APA Style

Science Buddies Staff. (2020, June 23). Measuring the Speed of 'Light' with a Microwave Oven. Retrieved from https://www.sciencebuddies.org/science-fair-projects/project-ideas/Phys_p056/physics/measuring-the-speed-of-light-with-a-microwave-oven

Last edit date: 2020-06-23

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FAQs

Why you could use the microwaves to test for the speed of light? ›

Your microwave oven is producing microwaves vibrating at a certain frequency. This frequency can be found written on the back of your microwave oven. The wavelength depends on how rapidly the wave is vibrating (the frequency) and how fast it is moving. As it is a type of light it moves at the speed of light.

How can you measure the speed of light? ›

After Maxwell published his theory of electromagnetism, it became possible to calculate the speed of light indirectly by instead measuring the magnetic permeability and electric permittivity of free space. This was first done by Weber and Kohlrausch in 1857. In 1907 Rosa and Dorsey obtained 299,788 km/s in this way.

How do you measure the speed of light in a microwave chocolate? ›

This means that the microwaves move up and down 2.45 billion times per second. Check in your microwave manual if you're not sure of the frequency. Multiply the distance between the spots on the chocolate bar by two. Multiply that by 2,450,000,000 (2.45 gigahertz expressed as hertz).

What is the most accurate way to measure the speed of light? ›

The speed of light could then be found by dividing the diameter of the Earth's orbit by the time difference. The Dutch scientist Christiaan Huygens, who first did the arithmetic, found a value for the speed of light equivalent to 131,000 miles per second. The correct value is 186,000 miles per second.

Does microwave travel speed of light? ›

As all electromagnetic radiation, microwaves travel at the speed of light (c). A wavelength (l) is defined as the distance between two peaks (or two troughs) of the wave.

What is the purpose of the light in the microwave? ›

Theory: Microwave ovens use light in the microwave part of the EM spectrum to cook food. The microwave photons reflect off the walls of the oven and can interfere with one another.

Why is it impossible to measure light speed? ›

We just cannot measure the speed of light in one direction because relativity prevents us from maintaining synchronised clocks. The result is that the speed of light c is really the average speed over a round-trip journey, and that we cannot be certain that the speed is the same in both directions.

Which device we can measure speed of light? ›

The Fizeau–Foucault apparatus is either of two types of instrument historically used to measure the speed of light. The conflation of the two instrument types arises in part because Hippolyte Fizeau and Léon Foucault had originally been friends and collaborators.

What tool is used to measure the speed of light? ›

A photometer, generally, is an instrument that measures light intensity or the opticalproperties of solutions or surfaces.

What are two ways to measure speed? ›

Vehicle Speed Measurement Methods
  • Speedometer Clocks.
  • Radar.
  • Average Speed Computers.
  • LIDAR (Light Detection and Ranging)
  • Aircraft.
  • Photo Radar.
  • Drone Radar.
3 Nov 2016

What is the speed of a microwave? ›

Model: Microwaves are electromagnetic waves that travel with a speed of 3 × 108 m/s.

How has the speed of light been measured experimentally? ›

The speed of light was measured using the Foucault method of reflecting a beam of light from a rotating mirror to a fixed mirror and back creating two separate reflected beams with an angular displacement that is related to the time that was required for the light beam to travel a given distance to the fixed mirror.

What is the frequency of microwave light? ›

Microwaves are defined as electromagnetic radiations with a frequency ranging between 300 MHz to 300 GHz. In contrast, the wavelength ranges from 1 mm to around 30 cm.

What are the three ways to measure light? ›

The 3 units of measurement of illumination
  • Lumen (Lm): A lumen is the amount of visible energy that we can actually measure. ...
  • Lux (Lx): one lux is the equivalent of the energy produced by one lumen incident on a surface of 1 m2.
  • Candela (Cd): is the basic unit that measures luminous intensity.
26 May 2022

Is a microwave faster than the speed of light? ›

A microwave oven works by reflecting microwave radiation around the oven space, creating standing waves that zap energy into your food to heat it up. These microwaves travel really fast. In fact, they travel at the speed of light (as do all the other waves on the electromagnetic spectrum).

Does a microwave produce light energy? ›

They are shorter than radio waves but longer than infrared radiation and waves in the visible spectrum. Because they have a longer wavelength than the visible spectrum, they do not produce visible light energy and we cannot see them!

Do microwaves use light waves? ›

Microwave ovens use electromagnetic waves that penetrate food, causing some molecules to vibrate and generate heat which is transferred throughout the food. Learn more about the electromagnetic spectrum.

What type of light is in a microwave? ›

Microwaves fall in the range of the EM spectrum between radio and infrared light.

What type of light does a microwave use? ›

Microwaves are a form of "electromagnetic" radiation; that is, they are waves of electrical and magnetic energy moving together through space. Electromagnetic radiation spans a broad spectrum from very long radio waves to very short gamma rays.

Can humans ever achieve the speed of light? ›

Based on our current understanding of physics and the limits of the natural world, the answer, sadly, is no. According to Albert Einstein's theory of special relativity, summarized by the famous equation E=mc2, the speed of light (c) is something like a cosmic speed limit that cannot be surpassed.

Could anything go faster than the speed of light? ›

So, according to de Rham, the only thing capable of traveling faster than the speed of light is, somewhat paradoxically, light itself, though only when not in the vacuum of space. Of note, regardless of the medium, light will never exceed its maximum speed of 186,282 miles per second.

Is there anything faster than the speed of light? ›

As a vacuum is devoid of such particles, light can attain its maximum velocity, which, as far as we know, cannot be surpassed. However, light travels at about 0.75c (75% light speed) through water. Some charged particles can move faster than 0.75c in water and therefore travel faster than light.

How accurate is the measurement of the speed of light? ›

He estimated the speed of light at 185,000 miles per second (301,000 km/s) — accurate to within about 1% of the real value, according to the American Physical Society (opens in new tab).

What materials do you need to measure speed? ›

Speed Technology

Police use RADAR and LIDAR to measure traffic speed. Cars have speedometers for travel speed and tachometers for engine speed. Accelerometers are also used with car speed measurements.

Which method is used to determine the speed? ›

To work out speed, divide the distance of the journey by the time it took to travel, so speed = distance divided by time. To calculate time, divide the distance by speed. To get the distance, multiply the speed by time.

Can you measure speed of light in one way? ›

We just cannot measure the speed of light in one direction because relativity prevents us from maintaining synchronised clocks. The result is that the speed of light c is really the average speed over a round-trip journey, and that we cannot be certain that the speed is the same in both directions.

What machine is used to measure the speed of light? ›

The Fizeau–Foucault apparatus is either of two types of instrument historically used to measure the speed of light. The conflation of the two instrument types arises in part because Hippolyte Fizeau and Léon Foucault had originally been friends and collaborators.

How did James Bradley calculate the speed of light? ›

Bradley used the angle of displacement measured from Earth as well as the relative velocity of Earth to calculate the speed of light. The angle of aberration is related to the ratio between Earth (observer)'s relative speed to the speed of light.

Is it impossible to measure the speed of light? ›

Since 1983 the metre has been defined as the distance traveled by light in vacuum in 1⁄299,792,458 second. This means that the speed of light can no longer be experimentally measured in SI units, but the length of a meter can be compared experimentally against some other standard of length.

How did Albert Michelson measure the speed of light? ›

He made use of a special eight-sided revolving mirror and obtained a value of 299,798 km/sec for the velocity of light. To refine matters further, he made use of a long, evacuated tube through which a light beam was reflected back and forth until it had traveled 16 km through a vacuum.

Has anyone measured the speed of light? ›

But several physicists have pointed out that while relativity assumes the vacuum speed of light is a universal constant, it also shows the speed can never be measured. Specifically, relativity forbids you from measuring the time it takes light to travel from point A to point B.

How did Galileo try to measure the speed of light? ›

Galileo supposedly attempted to quantify the speed of light, by using distant lanterns with shutters, which an assistant opened at specified times. Galileo would try to record how long it took light to get to him from across the field on which the experiment was done.

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