Editing The Speed Of Light From Your Microwave

{| class="wikitable" style="color:black; background-color:#ddd; margin-left: auto; float:right"
| [[Astronomy]], [[Physics]]:
| The Electromagnetic Spectrum, Speed of Light
|-
| Grade Range:
| [[Elementary School]], [[Middle School]], [[High School]]
|-
| Format:
| [[Hands-on]], [[Stage]]
|}

This demonstration provides kids with a simple and sticky way to measure the speed of light on their own. Be sure to have a way to dispose of the marshmallows before performing this demonstration.

== Materials ==

* Microwave
* Marshmallows
* Microwave Safe 8x8 Baking Dish
* Ruler
* White Board & Markers (Stage)
* Paper & Pencils (Hands-on)

== Safety Precautions ==

Please read the General Safety Precautions section of the [[Demonstration Safety]] page before performing this demonstration.

== Demonstration ==

;Presentation (Stage):
# Announce to the audience that you can calculate the speed of light using marshmallows and a microwave. Ask the audience if they have heard of the electromagnetic spectrum. If they have, ask them what it is, and what kinds of waves are on the spectrum.
# Put a single file line of marshmallows on the baking plate, being sure that they fill the dish. Remove the turntable from the microwave, and set the baking dish in so it won't turn. Microwave the marshmallows for 1-2 minutes, or until you see a standing wave pattern in the marshmallows. Remove them from the microwave and point out the wave pattern to the audience.
# Use the ruler to measure half a wavelength, and look up the microwaves frequency on the back of the unit. Write both numbers on the board with their units, with wavelength in cm and frequency in hertz or 1/s. Multiply the numbers together, and you should get a number close to the actual speed of light, 3 * 10<sup>8</sup> m/s!

;Presentation (Hands-on):
# Set up the microwave and remove the turntable. Set out the marshmallows, baking dish, pencils, paper, ruler and calculator.
# When students come up, Arrange the marshmallows on the baking tray so there is a straight line of them across it. Ask the students if they know of the electromagnetic spectrum, and if so to name some of the waves on the spectrum.
# Give each student a pencil and paper, and let them know that you will work together to calculate the speed of light using the microwave and marshmallows. Put the baking tray in the microwave, setting it so it won't rotate, and turn it on for 1-2 minutes, or long enough to make a standing wave pattern in the marshmallows. Remove them from the microwave and point out the pattern to the students.
# Use the ruler to measure half a wavelength in cm, and have the students write down the number and multiply it by two to get a whole wavelength. Have them copy down the frequency from the microwave in hertz. Convert the wavelength to m, and then multiply it by the hertz to get a number close to the speed of light, 3 * 10<sup>8</sup> m/s!

== Why This Works ==

===Short Explanation===
The ''Electromagnetic Spectrum'' is a wave spectrum that outlines all known ranges of electromagnetic radiation. This spectrum includes visible light, infrared and ultraviolet light, radio waves, x-rays, gamma rays, and even microwaves! All of the types of waves on the Electromagnetic Spectrum travel at the speed of light, or 3 * 10<sup>8</sup> m/s. This is extremely fast, capable of getting from one side of the earth to the other in less than <sup>1</sup>/<sub>20</sub> of a second! To measure how fast electromagnetic waves travel, we need to know two numbers: the frequency and their wavelength. ''Frequency'' is how many waves are produced per second, and is measured in Hertz. ''Wavelength'' is how long each wave is, and is measured in Meters. We can get both of these numbers for microwaves using a microwave oven.

The marshmallows will be struck by the microwaves and cooked while the microwave oven is on. Since they aren't moving, they will be cooked according to what part of the wave hits them, and therefore copy the wavelength. All microwaves list the Hertz they use on the back, usually in Gigahertz, so by multiplying these numbers together one will find the speed of the microwaves. The number calculated will not be the exact speed of light, but it should be within reasonable error. 

===Full Explanation===
The ''Electromagnetic Spectrum'' is the spectrum of wavelengths which are all known types of electromagnetic radiation. These wavelengths include radio waves, visible light, infrared and ultraviolet light, x-rays, gamma rays, and microwaves. All the waves on the electromagnetic spectrum can be affected or generated by other forms of electromagnetism, such as magnets and circuits. Also, every type of wave on the spectrum moves at the same speed as light, at 3 * 10<sup>8</sup> m/s. This property of electromagnetic waves is what makes them useful for communication no matter where you are in the world, since light can travel the diameter of earth in less than <sup>1</sup>/<sub>20</sub> of a second!

To measure how quickly a wave is moving, you need to know the frequency and the wavelength. ''Frequency'' is the number of waves per second, and is measured in Hertz. ''Wavelength'' is the length of the wave from one peak to the next, and is measured in meters. This shows us how we can measure the speed of electromagnetic waves:

{| class="wikitable" style="color:black; background-color:#ddd; text-align: left; margin-right: auto"
| '''v'''<sub>l</sub> = '''''f''''' * '''λ''' = <sup>1</sup>/<sub>y seconds</sub> * ''x meters''
|-
| '''v'''<sub>l</sub>: Velocity
|-
| '''''f''''': Frequency
|-
| '''λ''': Wavelength
|}

Since velocity is meters per second, multiplying the two numbers will give the speed of microwaves. The value will be within error of the speed of light, and could be made more precise with more accurate tools for measurement. An important thing to note is that this equation shows an important property of waves: the frequency of a wave is ''inversely proportional'' to the wavelength. If one value is increased, the other has to be decreased. This property is also why electromagnetic radiation with lower wavelengths can be dangerous in high doses; since the wavelength is short, the frequency is high, which means that it has higher energy as well. This is also why we don't hear concerns about radio waves; They have really big wavelengths, which means they have low frequencies, and therefore low energy.

== Additional Information ==

* This demonstration pairs well with the [[Flame Tube]] as a way to talk about the types of waves.
* This demonstration is a part of the [[Astronomy Show]]