Science Buddies: "Ask an Expert"

Hello!!! My name is Anna and I am a grade 9 student. I chose your experiment "How Does Color Affect Heating by Absorption of Light?". I have been trying the experiment for a week, over and over again. I changed a few things though, such as doing the experiment in a dark room so no light affects it and doing all the colours including black and white at once, (we took a plate, and we hung a light bulb precisely in the middle, with the glass bottles touching the rim of the plate. We put the glass jars in at 1 minutes intervals (1 jar--start timer; 2 jar--1 min on timer; 3 jar--2 minute on timer....until we reach 9 jars) for 1 hour. Then we record the temperature, subtract the starting temperature from that, and we look at the increase of temperature in each jar.

This is where I ran into problems. In one trial, it states that red and violet absorb the most heat, and yellow and green absorb the least(the numbers were really close--0.2 degrees off). In trial # 2, there is no pattern in the numbers(we have the 6 visible spectrum colours, so we are comparing the numbers to the order of the colours). Trial 3 stated that green absorbed the most heat, then yellow and red absorbed the least.

The numbers hold no specific pattern--such as red to violet increasing; red to violet decreasing; or something to compare the wavelengths of the colours to heat absorption.

I was wondering if you could tell me the expected results, so i could actually know if the answers that I got were correct. I will continue doing trials, but so far, the temperatures are random numbers that confuse me.

I was also wondering if you could tell me how wavelengths affect the heat absorption. Do the reflect the heat (for example if red wavelengths are longer, will they reflect more heat?)

I am stressing a lot about this project because non of my results seem to compare. I tried so many different ways, including placing 5 red bottles around the lamp and measuring the different temperatures. The was no pattern, just random numbers.

My hypothesis is: If the colour's wavelength is longer, the object will absorb more heat.

Normally I would be asking my dad, but he is not here at the moment. I would really really really appreciate your help because I do not know what to do, with the science fair being so close---only a week away!!!!!!!


Many thanks,
Anna

Hello Anna,

Let's see if I can help here. If I understand your description of your experiment, I think your problem might be with the light and the way you have arranged your bottles around it.

This experiment will take a lot of energy to raise the temperature of the water. It's important to use a "heat lamp", not just a regular light bulb. Here's the kind of lamp you need:

http://www.amazon.com/WATTS-HOURS-LIGHT ... B000STDLFE

I got the idea that maybe you were using a regular light bulb when you said "we hung a light bulb". Even if you are using a real heat lamp, you won't be able to put a number of jars, or bottles, around it. You must shine the heat lamp directly at the side of the bottle or jar. Either the bottle or jar needs to be on its side with the heat lamp shining down on it, or the lamp must be shining sideways at the side of the bottle. You must direct the energy of the lamp directly at the jar.

You had the right idea about keeping the distance from the lamp to the jar the same for all your tests.

It seems to me you already know the expected results. Your hypothesis is: If the colour's wavelength is longer, the object will absorb more heat. That is your expected result. The actual amount of temperature rise you get on each sample will depend on a lot of things: the size of the jar, how much water is in it, the thickness of the paper you are using, the wattage of your heat lamp, how efficient the heat lamp is, and the distance between the heat lamp and the jar.

If you are using a good heat lamp, I wouldn't worry about working in the dark. The heating will come primarily from the infrared light from the heat lamp. There isn't much of that in a typical room.

I hope this helps.

Good luck