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Asked by lumiereclair to Mark, Matthew, Mike, Paul, Sabina on 14 Mar 2014.
Question: What is a fun experiment related to light that you can do at home, and what can you learn from it/what does it prove?
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Mike Lee answered on 14 Mar 2014:
Do you have any energy saving light bulbs? You need a spare one, not one attached to a light socket.
If you take a ballon, blow it up, and rub it in your air so that it becomes statically charged. You can tell this has worked if the balloon sticks to a wall.
Next, touch the balloon against the energy saving light bulb. Hopefully the bulb will light up for a fraction of a second!
This shows how electric charges on the balloon can be turned in to light. The electric charges jump to bulb which has a special coating. When charges hit this coating, the coating lights up!
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Paul Coxon answered on 17 Mar 2014:
This is a good one to show how and why we see red sunsets in the evening. It’s an effect called Tyndall Scattering.
You’ll need
a big empty fishtank
a torch
small glass of milk.Fill the tank or bowl with water and let it settle so it’s nice and still. Switch in the torch and hold it against the side of the tank so a narrow beam of light shines through the water. (Turn off the room lights/close the curtains so you can se the effect better.)
Add a little bit of the milk to the water and look at the beam of light again. From the side the light looks bluish, but looking directly at the beam it looks slightly yellow. If you add the rest of the milk and stir up the mixture until it’s all cloudy, the light beam looks very blue from the side, and orangey yellow looking directly at it. The torch beam is also spread out and much wider.
When you added milk to the water, milk contains many tiny particles of protein and fat suspended in water. These particles scatter the light and make the torch beam visible from the side. Different colours of light are scattered by different amounts. Blue light is scattered much more than orange or red light. Because we see the scattered light from the side of the beam, and blue light is scattered more, and the beam appears blue from the side. Because the orange and red light is scattered less, more orange and red light travels in a straight line along the beam of the torch. So when you look directly into the torch beam, it looks orangey.
This is why the sky appears orangey/pink/red at sunset. The sun is low in the sky and to to reach our eyes the sunlight has to pass through a large portion of the atmosphere. This contains lots of dust particles which scatters the light in a similar way to the particles of milk. When you look at the setting sun, it’s like looking directly into the beam from the torch: all the blue light is scattered out to the sides and you’re seeing the light that isn’t scattered ie the orange and red.
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Matthew Malek answered on 17 Mar 2014:
Fun experiment at home? Let’s see… how about we build a magnifying glass using only a pinhole in an index card?
You will need:
A 3 x 5 inch file card,
A straight pin or needle,
Aluminium foil,
A lamp with dim (10 to 25 watt) lightbulb,
Masking tape,
Scissors.Now, put it together by cutting a one inche square in the card. Tape a piece of the aluminium foil over the hole and use the pin to punch a hole in the center of the foil. (You can make a good pinhole by placing the foil on a thick piece of cardboard and rotating a needle.)
Hold the card near your eye and look at the lightbulb several feet away. Move closer to the bulb until you almost touch it, and notice the magnified writing on the bulb. Use the pinhole magnifier to examine other small brightly lit objects. You can, for example, examine a computer screen or a television screen up close using a pinhole magnifier.
Try using pins or needles with different diameters to make different-sized
holes. You might notice that the smaller the pinhole is, the dimmer your view. As the pinhole is made smaller, the image at first becomes sharper, but then is blurred by diffraction.You also asked what we can learn from this experiment. Good follow-up question! Here’s the answer:
This “pinhole magnifier” works on a very simple principle: The closer you get to an object, the bigger it looks to you. This is because the closer you are to the object, the larger the image the object forms on your retina. Unfortunately, however, there is a limit to this. If you get too close to the object, your eye is not able to bend some of the light rays enough to obtain a focused image. As a result, the image becomes blurry or fuzzy. The pinhole magnifier gets around this problem by limiting the rays that come to you from each part of the object.
Alas, there is a trade-off between the resolution, or sharpness, of the image and its brightness. A tiny pinhole produces a very sharp image, but because it cuts down on the number of rays that enter your eye, the pinhole makes the object look much dimmer.
By using a pinhole magnifier, nearsighted people who normally see things fuzzily at a distance will be able to see them clearly; likewise, farsighted people who normally see things fuzzily close up will be able to see them clearly.
Pretty nifty, isn’t it?
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Mark Jackson answered on 17 Mar 2014:
Put on a pair of NICE sunglasses and look at an LCD computer screen. You probably see the screen is there but just dark. Now rotate the screen, and it will become dimmer until at some point it just disappears completely. This is because light coming from your screen is “polarized,” meaning that the waves have a specific direction. Your eye doesn’t usually care too much about this, but nice sunglasses do: they have a filter to prevent waves polarized at a certain angle – or glare – from getting in.
Speaking of polarized light, today was a physics announcement of historic proportions: the BICEP experiment measured polarized light from the Big Bang, which can only by caused gravitational waves. If true, this may be the earliest signal from the Big Bang humanity can ever observe. That only happens once.
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