Measuring the Speed of Light with a Microwave Oven_Science Fair Project

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Measuring the Speed of Light with a Microwave Oven

Maria Isabel Suarez IB Biology 2 Period 3 November 7, 2011 Science Fair Project

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Problem Statement Does measuring the speed of electromagnetic waves in the microwave portion of the spectrum by measuring the spacing between hot spots in a microwave oven will help me prove and understand the speed of light?

Background Information 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.

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.

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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. 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 chocolate bar.

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 = fλ.

Hypothesis If we find out what are the wavelength and the frequency, then we can find the speed of the wave, and since this is an electromagnetic wave, which is just the same as light, we can find out the speed of light.

Abstract 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. The purpose of my experiment was to test and prove the speed of light with a homemade experiment. I used the following procedures to do my experiment; I used the frequency of my microwave (2.45Ghz), which was given to me, and what was left was to measure the wavelength and that will guide us to obtain the speed of light. A wavelength is the distance between two peaks. When we measure the wavelength on the chocolate bar, we can only physically measure half of it, so it is necessary to multiply that by 2 to get the full wavelength. The data I collected was fairly accurate; there was a 6.3% error, which is very good for a homemade experiment. This data helped me with my conclusion which was that the speed of light can be tested and proven with many items that can be easily found at home, it is crucial to have the frequency, that’s obtained from the microwave oven itself and test properly the chocolate bars in order to achieve the purpose of it, get the speed of light.

Variables Independent: Time of chocolate bar heating Dependent: The chocolate bar (KitKat) and microwave oven

  Control

No heating temperature

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Constant The brand of chocolate bar, brand of the microwave oven, material of the plate used and temperature of the room.

Materials  Microwave oven (GE)  Plate (safe for use in microwave)  Oven mitts  2 Chocolate bars (KitKat)  Ruler  Calculator  Napkins  Camera Procedures 1. Gather all materials 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.

(Note: 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 chocolate 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 chocolate.)

3. To sample over the largest area possible, use a plate that is close to the inside dimensions of the microwave.

4. Line the chocolate bars on the middle of the plate that are at least 12 cm in diameter (in length).

5. Put the plate in the oven, close the oven door, and cook the chocolate bar.

6. Experiment to find the ideal cooking time for your particular oven. 1 minute and 30 seconds may be a good starting point. If the chocolate bar is completely melted, start over and decrease the time. If the chocolate bar is still totally solid (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 none melted chocolate bars.

7. The ideal result is to have the chocolate bar that is partially melted in some places, and nearly completely melted in other.

8. Use oven mitts to remove the plate from the oven. Be careful not to move the chocolate bar on the plate. Allow the plate to cool.

9. Measure the spacing between the cooked portions of the chocolate bar.

10. The centers of the cooked portions will not be clearly defined.

11. The goal in making this measurement is to find: the average distance between the cooked portions and an estimate for the error of your measurement.

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12. Using the cooked portions of the chocolate bar to measure the distance between "hot spots" in the microwave oven.

13. Measuring the "center-to-center" distance between adjacent cooked portions will give you the average spacing of the hot spots.

14. 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.

15. Clean and dry the plate, and repeat the experiment at least three times.

16. Look at the label on the back of the microwave to find the frequency of the microwave radiation the oven produces or in the user's manual for the oven.

17. The spacing of the hot spots will be equal to one-half of the wavelength of the microwaves.

18. 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.

Data

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Calculations 6.5 cm * 2 * 2,450,000,000 c/s = 31, 850,000,000 cm = 318,500,000 m/s Speed of light: 299,792,458 m/s 318,500,000 - 299,792,458 / 299,792,458 * 100% = 6.3% error Results In this experiment of Measuring the Speed of Light with a Microwave Oven, I used the frequency of the microwave, which I knew about, since it’s given to me in the back of the microwave (2.45Ghz), then what was left to do was find the wavelength, which was 6.5cm, then I multiplied that by 2 to get the full wavelength. Then I multiplied that by 2,450,000,000 c/s or 2.45Ghz, obtaining 31, 850,000,000 cm, which I then converted to 318,500,000 m/s. The speed of light, measured by real scientists, is 299,792,458 m/s. To find the margin of error, meaning to justify is the difference is significant I did the following, 318,500,000 - 299,792,458 / 299,792,458 * 100%. This drove me to conclude that 6.3% was my margin of error, which is pretty accurate for a homemade experiment.

The 13cm chocolate bar melted in two points, where I was able to measure with a ruler in centimeters. The measurement obtained from the experiment was a 6.5cm wavelength distance.

Conclusion In this experiment, we investigated the speed of light with a microwave oven. The hypothesis of this experiment was accurate, it expressed that if we find out what are the wavelength and the frequency, then we can find the speed of the wave, and since this is an electromagnetic wave, which is just the same as light, we can find out the speed of light. In this experiment, I used the frequency of the microwave, which I knew about, since it’s given to me in the back of the microwave (2.45Ghz), and then what was left to do was find the wavelength.

The major finding was that speed of light can be tested with a microwave oven’s wavelengths and its frequency. Light is a form of electromagnetic wave and in order to know the speed we need to know the wavelength and its frequency. It could be said that the experiment can be realized more than the three times I developed it. The purpose of this project was 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.

My findings are compared with other researches in the way that we can test the speed of light in many different ways, that it can be tested with different types of food besides chocolate such as, bread and/or eggs. The experiment can be improved by using a thicker and longer chocolate bar, and even maybe a larger microwave oven that contains more space and always make sure the chocolate is standing still and not rotating.

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What happens is that the waves in the microwave pass from one side to the other if the plate is turning what’s going to happen is that its going to heat up the entire bar homogeneously, which we don’t want that, we want to see where the wave hits the chocolate, letting us calculate the speed of light.

Applications This experiment can be applied to future understanding of how speed light works like and explained with physics and food in a very creative way. However, this experiment is mostly to test, prove and understand the process of the speed of light, its frequency and wavelength, the distance between two peaks. It will be helpful for those studying physics and lack of understanding and desire to learn the process. The speed of light is a topic that can be tested with home supplies and in a very short period of time.

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