|MadSci Network: Physics|
It seems to me that the key piece of information you need is the equation f = E / h which was created by the physicist Max Planck, and published in the year 1900. This equation was the starting point for the whole of Quantum Mechanics (Happy Centenary!), but fortunately the thing it describes is pretty simple: (Frequency) equals (Energy) divided by (Planck's Constant). (NOTES: Usually the equation is expressed as (Energy) equals (Planck's Constant) multiplied by (Frequency), but because of the lack of a unique and recognized-by-all multiplication symbol, I have opted for the divisive form presented above. Also, Frequency is usually symbolized by one of the letters of the Greek alphabet (nu), rather than the f above. But my simple text editor doesn't do Greek, so....) We are talking about the frequency and energy of a single photon of light. Frequency is measured in Hertz (cycles per second), and is directly associated with the color of light. Next, energy (when associated with photons) tends to be measured in terms of 'electron-volts', which is the amount of energy acquired by one electron as it accelerates across a distance of one centimeter, under the influence of one volt. This is a very small unit; an average photon of visible light carries roughly two electron-volts of energy (and radio-wave photons carry miniscule fractions of that). The most commonly used unit of energy larger than an electron-volt is the erg (the energy needed to accelerate one gram of mass such that its velocity changes by one centimeter per second). The erg is vastly larger than the electron-volt: one erg equals 6.242x10E11 (or 624200000000) electron-volts. Finally, there is Planck's Constant; it is simply 6.626x10E-27 (or 0.000000000000000000000000006626) erg-seconds. It is inherently just a description of how finely divisible is the "essence" of the Universe; a different value than the one it has could be associated with a radically different Universe than the one know. The very small value of Planck's Constant means we inhabit a very fine Universe (pun intended; a 'coarse' Universe likely would truly be a rough place for us to try to survive!). To be mathematically consistent, the measurement-units associated with frequency, energy, and Planck's Constant must match; thus I offer this minor conversion: Planck's Constant is 4.136x10E-15 (or 0.000000000000004136) electon-volt-seconds. From this you can see that even for an electron, Planck's Constant describes a fine state of affairs. ------------------------------- Your experiment is going to provide you with a wealth of research opportunities in a library (or on the Web). For starters, you will need data on the output of your sun lamp, in terms of how much energy is emitted at each color-frequency that you will be testing. (One source for such data is typically the manufacturer.) It would do your experiment no good to fail to take into account the fact that most incandescent light sources emit significantly less blue light than they emit yellow light. Then, for each frequency, this energy should be converted from, say, ergs per second into photons per second. Then, from the angles at which light leaves the sun lamp and reaches the liquid-containers, you must figure what portion of the photons actually arrive.... Next, you will need data on the exact spectral absorption signatures of each of the colored filters that you will be using. A filter that transmits red light generally does not transmit 100% of all frequencies (or even 100% of any single frequency) of red light, for example. But once you have the data, you can then compute how many photons per second of each freqency pass through the filter and into the liquid. You will need similar absorption data for each of the liquids you plan to test. Keep in mind that since the liquids you mentioned (water, alcohol, and salt water) are pretty transparent, you may have to operate your experiment for a lengthy period in order to be able to measure the results. The PURPOSE of gathering all the preceding information is to become able to predict the results. It is by comparing predictions to actual measurements that Science ultimately progresses, because when the results don't match, that means something new is waiting to be learned. Other factors to be wary of are: The background upon which the beakers rest; will it absorb light, grow warm, and directly influence the temperatures of the liquids? -- or will it reflect light, and thereby change the number of photons that you would expect to pass into the liquids? (Perhaps the beakers should be suspended away from any background.) What of the temperature of the surrounding air; how will its absorption of light from the sun-lamp affect the beakers? And what of the fact that alcohol (and to a lesser extent water) tends to evaporate easily? Your beakers may have to be sealed! -- since the experiment's duration may lead to less liquid being heated than you planned. There may be more things to keep track of than I have mentioned here. The longer the list, the more difficult the experiment -- but the greater the reward will be in a science fair. I wish you the best of patience, skill, care -- and luck.
Try the links in the MadSci Library for more information on Physics.