A Peep Into the Speed of Light

    May, 2015:

    Kids, did you know that you can calculate the speed of light using common materials in your kitchen? The speed of light is 299,792,458 meters per second, or 670,616,629 miles per hour. According to an entertaining NPR video from Skunk Bear, the speed of light is easy to calculate using Peeps® and a microwave oven.

    First, what are microwaves? Microwaves are a type of radiation and, like all radiation, microwaves are part of the electromagnetic spectrum. “Microwaves” also are kitchen appliances that heat food by exposing them to microwave radiation.

    What you’ll need:

    • chocolate, egg whites, cheese, marshmallows or something else that will melt easily and unevenly; Peeps are perfect.
    • flat-bottomed, microwave-safe oblong cake pan (11 x 8”).  A Pyrex® baking tray would work well.
    • oven mitts
    • microwave oven
    • ruler
    • calculator or basic math skills

    Like all waves, microwaves are defined by their frequency and wavelength. How do you determine the frequency of the radiation in your microwave oven? Look at the manufacturer’s sticker and the abbreviations MHz or GHz. (The hertz is the unit of measurement for frequency.) A common frequency value is 2,450 MHz, or 2.45 GHz. This means 2,450,000,000 Hz, or 2,450,000,000 cycles per second.

    How do you determine the wavelengths of the radiation in your microwave?

    1. Take a glass oblong cake-baking pan and pack it full of Peeps; different colors are fine.
    2. Heat the Peeps pan in the microwave on fairly low heat, without turning. Don’t heat it too much—you want it to warm unevenly and to have “hot spots”.
    3. Take out the plate and measure the distance between hot/gooey areas. Poke the Peeps with toothpicks to find the gooey areas. The average distance between these areas is about half a wavelength.
    4. Find the wavelength by multiplying the average distance by two.

    In our calculation the average distance between hot spots was about 6.1 centimeters. So, the wavelength was about 12.2 centimeters.

    Now multiply the frequency (2,450,000,000) by the wavelength. You should get pretty close to the speed of light in inches per second or centimeters per second.

    Use this site to convert inches-per-second to miles-per-hour:

    Multiply your answer by .01 to convert centimeters-per-second to meters-per-second. Using our data:

    • 12.2 x 2,450,000,000 = 29,890,000,000. That’s centimeters-per-second.
    • 29,890,000,000 x 0.01 = 298,900,000. That’s meters-per-second. And this is very close to the constant 299,792,458!

    Many thanks to David Czaplewski of Argonne National Laboratory for making us aware of this experiment.