Can you see the light? (p3)

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Jesús Manzaneque & María Montes

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Light and dark


The Science of Light


Experiments

Make your own rainbow
Learn how to make a rainbow with this science experiment. Using just a few simple everyday items you can find out how rainbows work.
What you'll need:
Instructions:
What's happening?
  • A glass of water (about three quarters full)
  • White paper
  • A sunny day
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  1. Take the glass of water and paper to a part of the room with sunlight (near a window is good).
  2. Hold the glass of water (being careful not to spill it) above the paper and watch as sunlight passes through the glass of water, refracts (bends) and forms a rainbow of colors on your sheet of paper.
  3. Try holding the glass of water at different heights and angles to see if it has a different effect.
While you normally see a rainbow as an arc of color in the sky, they can also form in other situations. You may have seen a rainbow in a water fountain or in the mist of a waterfall and you can even make your own such as you did in this experiment. 
Rainbows form in the sky when sunlight refracts (bends) as it passes through raindrops, it acts in the same way when it passes through your glass of water. The sunlight refracts, separating it into the colors red, orange, yellow, green, blue, indigo and violet.
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What absorbs more heat?
When you're out in the sun on a hot summers day it pays to wear some light colored clothes, but why is that? Experiment with light, color, heat and some water to find out.
What you'll need:
Instructions:
What's happening?
  • 2 identical drinking glasses or jars
  • Water
  • Thermometer
  • 2 elastic bands or some sellotape
  • White paper
  • Black paper
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  1. Wrap the white paper around one of the glasses using an elastic band or sellotape to hold it on.
  2. Do the same with the black paper and the other glass.
  3. Fill the glasses with the exact same amount of water.
  4. Leave the glasses out in the sun for a couple of hours before returning to measure the temperature of the water in each.
Dark surfaces such as the black paper absorb more light and heat than the lighter ones such as the white paper. After measuring the temperatures of the water, the glass with the black paper around it should be hotter than the other. Lighter surfaces reflect more light, that's why people where lighter colored clothes in the summer, it keeps them cooler.
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Bend a Straw with Your Eyes
Using the power of your eyes, bend a straw sitting in half a glass of water without even touching it! It sounds like magic but it's really another amazing scientific principle at work.
What you'll need:
Instructions:
What's happening?
  • A glass half filled with water
  • A straw
  • 2 eyes (preferably yours)
  1. Look at the straw from the top and bottom of the glass.
  2. Look at the straw from the side of the glass, focus on the point where the straw enters the water, what is strange about what you see?
Our eyes are using light to see various objects all the time, but when this light travels through different mediums (such as water & air) it changes direction slightly. Light refracts (or bends) when it passes from water to air. The straw looks bent because you are seeing the bottom part through the water and air but the top part through the air only. Air has a refractive index of around 1.0003 while water has a refractive index of about 1.33.
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