Reflection and absorption
Hot shoes!
Background
If I had understood
reflection and absorption
of white light and how colors affect these two processes, I would have also understood my discomfort!
What am I talking about? When I was at school, I volunteered for cadets. This is where you learn how to march, as they do in the army. The drilling used to take place on our school field, in mid-day sun. Marching wasn't the problem, it was the standing. The most uncomfortable part of my body were my feet – why? - we had to wear BLACK shoes.
So what has this got to do with this experiment about reflection and absorption?. Everything! To find out why ...
Let's do science...
The Experiment
We know that white light comes from the sun and carries with it – energy! This energy, when it reaches objects on earth, is converted into heat.
So whatever sunlight touches will be heated up, either more, or less. There are a couple of factors that will result in one object being hotter than another – firstly the amount of sunlight hitting that object (direct, midday sunlight will have more energy than sunlight a dusk or dawn) and the color of the object.
This experiment is going to focus on how color affects the temperature of an object.
The Aim
To determine how color (because of reflection and absorption) affects the temperature of objects.
Equipment Needed
Six glass bottles
Tap water
Five colored sheets of paper – white, black, red, green, blue
Cellotape
Scissors
A sunny spot - i.e. in direct sunlight (such as a windowsill)
A thermometer that can be used to measure the temperature of water
Method
Wrap and fix a different colored sheet of paper around each of 5 of the bottles. Leave the last one without any paper around it. This is your control.
Fill each of the bottles with tap water.
Take and record the temperature of the water in the first bottle. Give the thermometer 2 minutes to get the reading.
Place that bottle in a sunny spot.
At the same time place the thermometer in the second bottle.
Exactly 2 minutes later, record the temperature for this bottle and place it in the sunny spot. Then place the thermometer in the third bottle.
2 minutes later place the third bottle in the sunny spot. Continue taking “zero time” temperature readings and placing bottles in the sunny spot every 2 minutes until all the bottles are in the sunny spot.
When you place the last bottle in the sunny spot, put the thermometer in the first bottle again. (This means that the first bottle would have been sitting in the sun for 12 minutes.)
After 2 minutes, read and record the temperature, and then place the thermometer in the second bottle.
Continue to do this until you have a 12 minute temperature for all the bottles.
Then start again at the first bottle and continue for all the bottles (this will be the 24 minute reading).
Continue in this manner until you have 6 readings for each bottle. At the end you should have readings at 0, 12, 24, 36, 48 and 60 minutes for each bottle. The whole exercise will take 1 hour 12 minutes.
If this explanation has totally confused you, print out
this table
which will help you organize your experiment and capture your data.
Results
This is what you should see happening:
The temperature of the water in all the bottles will go up.
Over time, each bottle will reach a temperature where it will no longer go up.
The bottles with the darker colored paper around them will end up with a higher temperature than the lighter colored bottles.
The Conclusion
The color of an object (in this case the bottles) will determine the amount of reflection and absorption of white light that happens to that object. Energy is absorbed by the bottles in varying degrees, with the darker colors absorbing more energy than the lighter colored bottles and therefore the darker colors will heat up more.
You will end up with data from which you can create a chart for your display. Check out
How to use charts
to see what chart to use for this result and how to draw it.
And so now you know why reflection and absorption are responsible for why my shoes got so hot!!!
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