All About Microwaves

Microwaves are in almost everyone’s kitchen. But, they have some pretty nasty myths associated with them. Many people think that microwave ovens radiate food and that radiation stays in the food. Some people think that you cannot put anything metal in a microwave. Many people also believe that the power function of the microwave changes the output power . Often people say that microwaves cook from the inside out. These are all common misconceptions about microwaves. Here is a link to Wikipedia’s page on microwave ovens . There is some pretty neat history there that tells you all about how microwaves were invented just 65 years ago and how they became so commonplace in our homes. Despite all of the misconceptions, microwaves do have their limitations and dangers. These experiments that you can do at home are safe, fun and will show you what’s true about microwaves.

Let’s start by gathering your equipment and ingredients. Always gather everything first and read all of the instructions before you start. That way you won’t be scrambling for an ingredient or utensil at a critical moment. Remember, ask for an adult to help, there may be hot items, sharp tools or things to high to reach safely.

Equipment:

Plastic tray that fits neatly inside of your microwave oven
Incandescent Light bulb, the higher the watts the better, I use a 200 watt bulb, but a 60 or 80 watt bulb will work too.
Magnet
10 inch balloons. (If you are allergic to latex, disposable nitrile gloves work too)
Funnel
Measuring cup
Ruler with centimeters
Stop watch or watch with second hands
Paper to record results
Microwave oven (of course!)

Ingredients:

Mini Marshmallows
Water

This is a great time to make marshmallow rice crispy treats too. I have provided a recipe and instructions at the bottom of the page


Functions of power:

Let’s start by learning about the power functions of your microwave. You will probably need an adults help to set the timer here. Often you enter the time you want to cook your food, hit power, enter the power setting and then hit start. Many people believe that by entering in a particular power setting, usually 10 through 100 in increments of 10, or 1 through 10 in increments of 1, is changing the output of the microwaves. Microwave ovens fire microwaves at the same frequency and power every time, by entering in power of 30 is actually changing how long the microwaves are fired. The additional humming you hear is a fan used to distribute heat. Here is how we can demonstrate that:

1. Fill a balloon or disposable glove using your funnel with about ¼ cup of water. Tie off the balloon so there is very little air in it.

2. Place the balloon in the microwave for 2 minutes on the lowest power setting, usually 1 or 10, and time it until the balloon inflates. Time how long it takes to inflate. Notice there is a audible click and then the balloon will start to deflate (shrink). Time it from when it begins to deflate to when it begins to inflate. Stop the microwave. Record your results.

3. Allow your microwave and balloon to cool for about a minute.

4. Repeat the timing for each power setting on your microwave.

When you are finished with all of the power settings you will have a chart that shows the length of time until the water in your balloon is hot, and then a length of time in between cycles of heating. Notice that the higher power heats more frequently than lower power settings. The hum you hear in between heating cycles is a fan helps the heat to distribute in the food you are cooking. Yum Balloons! Think about some things you commonly put in a microwave. How can you use what you have learned to cook them better? Hot dogs and potatoes are just a couple things you can try out and find better ways to cook.


Cooking at the Speed of Light:
   
Even though you can’t see them, microwaves are a form of light, just a different part of the light spectrum than visible light. You can even use your microwave to measure how fast light moves. This experiment will also show you where in your microwave heating occurs best, and why most new microwaves have a rotating tray.

1. Start by removing the rotating plate in the bottom of some microwaves. It should just slip out. If your microwave does not have one, great, skip this step.

2. Now fill your plastic tray with marshmallows. Be sure to cover all of the tray with the marshmallows, fairly close together, but in a single layer as shown in the picture.                                                                                                                
3. Heat the marshmallows on full power for about 1 minute. Notice that several peaks start to raise. These peaks should form a line, kind of like ocean waves. After 3 or 4 peaks form and, measure in centimeters with your ruler from peak to peak and record your result. Do this quickly before the peaks deflate(shrink) too much. If you have a plastic ruler you can simply lay it across the marshmallow at the front or back, not the middle

4. Most microwaves cook at 2450 MHz. This is called the frequency of the microwaves, they are measured in cycles per second. Some cook at a lower 900 Mhz, others, usually commercial and in Europe, cook at a much higher frequency. If you are not sure on the frequency, check on the back, it might be 2.45 GHz, that’s the same thing as 2450 MHz, it is a fancy way of saying 2,450,000,000 times(cycles or waves) per second. You can find the speed of light and demonstrate that your microwaves are moving that fast by multiplying the MHz by the distance in centimeters you found between each peak (the wave length).

2,450,000,000 times your wave length in cm = the speed of light in centimeters per second if you divide by 100,000 to convert to kilometers, you should get about 294,000 kilometers per second . Wow, that’s cooking fast.

Speaking of light:

Everyone says you cannot put metal in the microwave. Well, that’s only kind of true. The inside of your microwave is metal, stick a magnet on it and check for yourself (remove the magnet before using your microwave). Metal is what keeps the microwaves from leaking out. The perforated screen on the door is metal too; the holes in it just the right size and distance apart that visible light waves can go through, but microwaves cannot. What microwaves do with metal actually depends on the shape of the metal object. If the object comes to a point or a sharp edge, like most things in our kitchens do, the metal resonates (vibrates at the same frequency as your microwaves). As it resonates, electricity is produced at the sharp edges, causing a spark, that’s why the hole on the door are round. Here is a neat way to see that in action without damaging your microwave. DO NOT try this with anything else as other objects might cause damage to your microwave oven. Simply place the light bulb on the tray in your microwave and heat for 10 to 20 seconds at a lower power setting, 3 or 30 works great. Stop it right after it lights up.

And now for something yummy after all that experimenting:

Rice Crispy Treats:
                    

1 16 oz bag marshmallows (includes the marshmallows from above)

3 oz butter cut into pieces

8 cups Rice Crispy Cereal

6 oz Chocolate Chips (optional)

4 oz dried blueberries or strawberries (cut the strawberries into pieces)(optional)

1 tsp Real Vanilla Extract
   

1. Grease a rectangular baking pan. Pan spray works great, or rub it with cold butter. Also grease a rubber spatula for stirring and a flat metal spatula to even everything out at the end.

2. Combine marshmallows, butter and vanilla in a microwave safe bowl. Microwave on high for 3 to 4 minutes, stirring after every minute.

3. Add the rice crispy cereal stir to combine, then add dried fruit or chocolate if desired.

4. Fill the greased pan with the mixture and press into the pan with the metal spatula. Make sure they are even and fill the corners.