This week we're going to measure the speed of light using a chocolate bar and a microwave! Sounds impossible? Try it and see!
What you will need:
A large chocolate bar (at least 18cm by 8cm)
A piece of paper
A microwave oven
- Unwrap the chocolate and place it on the paper.
- If your microwave has a turntable, disable it by turning the glass upside down. Be very careful handling the glass plate - consider asking a grown up to do this for you.
- Put some water in the glass and put it at the back of the microwave.
- Place the paper with the chocolate bar in the microwave. Make sure that the longer side of the chocolate bar is parallel to the longer side of the microwave.
- Set the microwave for twenty seconds.
- Start the microwave, but make sure that you watch through the door.
- As soon as you see parts of the chocolate begining to melt, stop the microwave. NOTE: the chocolate will melt unevenly, so watch closely.
- Leave the chocolate on the paper and take it out of the microwave. Be careful because the chocolate will be hot.
- Put a toothpick in each soft, melted spot.
- Measure the distance between each toothpick and write it down.(Catherine Thomas, staff writer)
What's the Science? 科學原理
A microwave produces a series of standing waves to heat food. Normally the turntable moves round, ensuring that the food is heated uniformly. If it is disabled, hotspots will be created at the crest and the trough of the standing wave. In other words, the greatest heating (hotspots) occurs where the amplitude of the wave is the greatest. The water, oil and fat molecules in the chocolate will quickly melt under these circumstances. This allows you to measure the distance between each half wave (the distance between two toothpicks). One wavelength includes a crest and a trough. This is why you mulitply the distance between the toothpicks by two. Microwaves are electromagnetic waves. Electromagnetic waves travel at the speed of light. Therefore, if you can measure the wavelength of the standing wave in a microwave, you can calculate the speed of light using the formula c = l * f.
1. turntable n.
轉盤 (zhuan3 pan2)
2. disable v.i/v.t.
使失去能力 (shi3 shi1 qu4 neng2 li4)
3. parallel adj.
平行的 (ping2 xing2 de5)
4. melt v.t/v.i.
溶化 (rong2 hua4)
5. wavelength n.
波長 (po1 chang2)
6. frequency n.
頻率 (pin2 lu4)
7. decimal point n.
小數點 (xiao3 shu4 dian3)
8. standing waves n.
駐波 (zhu4 po1)
9. crest n.
頂點 (ding2 dian3)
10. trough n.
波谷 (po1 gu3)
11. amplitude n.
振幅 (zhen4 fu2)
12. electromagnetic wave n.
電磁波 (dian4 ci2 po1)
微波爐製造一系列的駐波來加熱食物。通常轉盤之所以旋轉，是確保食物受熱均勻。如果轉盤不動，熱點會在駐波的波峰或波谷處產生。換句話說，最大加熱處（即熱點）發生在波振幅最大處。巧克力中的水分子，油分子和脂肪分子在這些條件下會迅速地溶化。藉此你可以測量出每半個波長間的距離（即兩支牙籤彼此間的距離）。一個波長包括了一個波峰和一個波谷。這也就是為什麼兩支牙籤間的距離要乘以二的原因。微波是電磁波，以光速進行。因此，如果你能測量出微波爐駐波的波長，你就可以利用光速公式 c=l * f 計算出光速了。
The measurement 測量方式
The equation that defines the speed of light is c = l * f
c is the speed of light
l is the wavelength
f is the frequency
To find out the frequency of your microwave, look for a label on the inside of the door or the back of the microwave. If you can't find it, don't worry, nearly all microwaves operate at a frequency of 2.45 gigahertz. Therefore, frequency (f) = 2,450,000,000.
To work out the wavelength, take the distance between the
toothpicks and multiply it by 2 (see "What's the science" to see why).
This is the wavelength in cm. You want the wavelength in m so move the decimal point 2 places back (eg 6.0cm will become 0.06m).