Shine a light through polarized sunglasses and the brightness decreases. If you hold two pairs of sunglasses one way, the light then is completely blocked! Not only that, but when you insert a third pair in between the two allows light to pass through again! Spooky!
Materials
This is a recording of a recent live teleclass I did with thousands of kids from all over the world. I’ve included it here so you can participate and learn, too!
This class is all about Light Waves, Lasers and Holograms! This is a newly updated version of the older Light Waves and Lasers teleclass here.
We’re going to learn about the wild world of light that has baffled scientists for over a century. You’ll be twisting and bending light as we learn about refraction, reflection, absorption, and transmission using lenses, lasers, mirrors, and optical filters with everyday stuff like gummy bears, paperclips, pencils and water!
We’re going to learn how to build a projection hologram out of piece of old plastic, make a laser microscope so you can see tiny little microscopic creatures, bend laser light to follow any path you want without using mirrors, and finally understand how glow in the dark toys really work on the subatomic level. Are you ready?
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Particles that move close to the speed of light have a different equation for momentum in order for momentum to be conserved using Einstein’s relativistic equations. The speeds of large objects like baseballs, bullets, and satellites are so much less than the speed of light so we can use Newton’s equations for it. If you’re studying electrons and other subatomic particles, you must use equations from special relativity.
Have you ever wondered why you just can’t just shine a flashlight through a lens and call it a laser? It’s because of the way a laser generates light in the first place.
The word LASER is an acronym for Light Amplification by Stimulated Emission of Radiation.
That’s a mouthful. Let's break it down.
Let's do an experiment that shows you how a laser is different from light from a flashlight by looking at the wavelengths that make up the light.
Laser light is collimated, meaning that it travels in parallel rays. Here’s a really cool experiment that will show you the difference between a non-collimated light, like from a flashlight and collimated light from a laser.
Ordinary light from a light bulb diverges as it travels. It spreads out and covers a larger and larger area the further out you go. A laser has little to no divergence, so we way that laser light is collimated.
Lasers light is different from light from a flashlight in a couple of different ways. Laser light is monochromatic, meaning that it’s only one color.
Laser light is also coherent, which means that the light is all in synch with each other, like soldiers marching in step together. Since laser light is coherent, which means that all the light waves peaks and valleys line up. The dark areas are destructive interference, where the waves cancel each other out. The areas of brightness are constructive interference, where the light adds, or amplifies together. LED light is not coherent because the light waves are not in phase.
Diffraction is how light bends as it passes through very narrow slits or around very thin objects like a hair. When light travels around a hair, two wave patterns form, and those waves interfere with each other constructively (they add together to form a bright region) or destructively (the cancel each other out and leave a dark spot).
This experiment looks at the light and dark areas of interference to determine the wavelength of a laser. You can do this for lasers that don’t have labels on them, so you really don’t know what wavelength they are!
Gummy bears are a great way to bust one of the common misconceptions about light reflection. The misconception is this: most students think that color is a property of matter, for example if I place shiny red apple of a sheet of paper in the sun, you’ll see a red glow on the paper around the apple.
Where did the red light come from? Did the apple add color to the otherwise clear sunlight? No. That’s the problem. Well, actually that’s the idea that leads to big problems later on down the road. So let’s get this idea straightened out.
If you’re scratching your head during math class, wondering what you’ll ever use this stuff for, here’s a cool experiment that shows you how scientists use math to figure out the optical density of objects, called the “index of refraction”.
How much light bends as it goes through one medium to another depends on the index of refraction (refractive index) of the substances. There are lots of examples of devices that use the index of refraction, including fiber optics. Fiber optic cables are made out of a transparent material that has a higher index of refraction than the material around it (like air), so the waves stay trapped inside the cable and travel along it, bouncing internally along its length. Eyeglasses use lenses that bend and distort the light to make images appear closer than they really are.
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The angle that the reflected light makes with a line perpendicular to to the mirror is always equal to the angle of the incident ray for a plane (2-dimensional) surface.
We’re going to play with how light reflects off surfaces. At what angle does the light get reflected? This experiment will show you how to measure it.
This simple activity has surprising results! We’re going to bend light using plain water. Light bends when it travels from one medium to another, like going from air to a window, or from a window to water. Each time it travels to a new medium, it bends, or refracts. When light refracts, it changes speed and wavelength, which means it also changes direction.
Most people know not to shine lasers into sensitive places like eyeballs, but very few people can tell one laser from another. The truth is that not ALL lasers are dangerous, and there are different classifications of lasers. The most important information you need about laser safety is printed right on the laser itself.
Basic Laser Guidelines for Safety:
1. Never look directly at the beam source, or aperture
2. Never point the beam at another person
3. Always be mindful of where a “bouncing beam” will land due to reflection
This set of experiments will show you the properties of light, including optics, diffraction, transmission, reflection, wavelength, intensity, and so much more. You’ll discover how light travels in a straight line, how light can turn a corner, split into several beams, and why objects can appear dark even when light is shining right on them.
Fluorescent minerals emit light when exposed to ultraviolet (UV) light, usually in a completely different color than when exposed to white light. UV is invisible to the human eye, and is the wavelength of light that is responsible for sunburns.
We’re going to use a laser pointer and a protractor to measure the microscopic spacing of the data tracks on a DVD and a CD. The really cool part is that you’re going to use an interference pattern to measure the spacing of the tracks, something that you can’t normally see with your eyes.
Interference is what happens when waves smack into each other. When the waves collide, if the two highest or two lowest points of the waves are lined up, then they add together to form a larger amplitude which is seen as a bright spot of light. However, if a peak and a trough line up, then they cancel each other out and there is a dark area in the pattern (see the dark spaces in the line?).
Have you ever wondered why the sky is blue? Or why the sunset is red? Or what color our sunset would be if we had a blue giant instead of a white star? This lab will answer those questions by showing how light is scattered by the atmosphere.
Particles in the atmosphere determine the color of the planet and the colors we see on its surface. The color of the star also affects the color of the sunset and of the planet.
Materials
Do you have thick or thin hair? Let’s find out using a laser to measure the width of your hair and a little knowledge about diffraction properties of light. (Since were using lasers, make sure you’re not pointing a laser at anyone, any animal, or at a reflective surface.)
If you’ve never done this experiment, you have to give it a try! This activity will show you the REAL reason that you should never look at the sun through anything that has lenses in it.
Because this activity involves fire, make sure you do this on a flame-proof surface and not your dining room table! Good choices are your driveway, cement parking lot, the concrete sidewalk, or a large piece of ceramic tile. Don’t do this experiment in your hand, or you’re in for a hot, nasty surprise.
As with all experiments involving fire, flames, and so forth, do this with adult help (you’ll probably find they want to do this with you!) and keep your fire extinguisher handy.
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Here’s what you need to do:
Let’s see how much you’ve picked up with these experiments and the reading – answer as best as you can. (No peeking at the answers until you’re done!) Just relax and see what jumps to mind when you read the question. You can also print these out and jot down your answers in your science notebook.
Click here for a printer-friendly version of the Unit 9: Light & Lasers Exercises.
Let’s see how much you’ve picked up with these experiments and the reading – answer as best as you can. (No peeking at the answers until you’re done!) Just relax and see what jumps to mind when you read the question. You can also print these out and jot down your answers in your science notebook.
Click here for a printer-friendly version of the Unit 9: Light & Lasers Exercises.
Let’s see how you did! If you didn’t get a few of these, don’t let it stress you out – it just means you need to play with more experiments in this area. We’re all works in progress, and we have our entire lifetime to puzzle together the mysteries of the universe!
Here’s printer-friendly versions of the exercises and answers for you to print out: Simply click here for printable questions and answers.
Let’s see how you did! If you didn’t get a few of these, don’t let it stress you out – it just means you need to play with more experiments in this area. We’re all works in progress, and we have our entire lifetime to puzzle together the mysteries of the universe!
Here’s printer-friendly versions of the exercises and answers for you to print out: Simply click here for printable questions and answers.
1. Light can change speed The word “LASER” stands for Light Amplification by Stimulated Emission of Radiation.
2. Light from a regular incandescent light bulb covers the entire spectrum as well as scatters all over the room. A laser beam is monochromatic – the light that shoots out is usually one wavelength and color, and is in a narrow beam.
3. Glass (like a window pane) and clear plastic (like a water bottle).
4. Take it in a steamy room, like just after a hot shower. Or aim it through a glass of water that has a drop of milk in it.
5. The laser beam hits a spinning mirror that’s off-center. The more angled the mirror mount, the larger the image that the laser traces out. Which is why this is a perfect project for kids – the sloppier they build it, the better the laser light show.
6. High-power CO2 lasers have an intense amount of heat that melts through metal. These aren’t the lasers we’re going to be working with! The lasers at the grocery store are Class I lasers, which will harm your eye if you stare into it without blinking once for at least 15 minutes. These ‘keychain’ lasers are Class II & III, some of which can overpower your retina in less than a minute, and the damage is irreversible. When I work with kids in a live Laser Lab class, I have a zero-tolerance rule (which is explained beforehand): if misused, I just walk over, take the laser without a word, and keep it. Class proceeds as normal, and it’s up to the kid to figure out how to finish the project.
Polarization has to do with the direction of the light. Think of a white picket fence – the kind that has space between each board. The light can pass through the gaps int the fence but are blocked by the boards. That’s exactly what a polarizer does.
When you have two polarizers, you can rotate one of the ‘fences’ a quarter turn so that virtually no light can get through – only little bits here and there where the gaps line up. Most of the way is blocked, though, which is what happens when you rotate the two pairs of sunglasses. Your sunglasses are polarizing filters, meaning that they only let light of a certain direction in. The view through the sunglasses is a bit dimmer, as less photons reach your eyeball.
Polarizing sunglasses also reduce darken the sky, which gives you more contrast between light and dark, sharpening the images. Photographers use polarizing filters to cut out glaring reflections.
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When light rays strikes a surface, part of the beam passes through the surface and the rest reflects back, like a ball bouncing on the ground. Where it bounces depends on how you throw the ball.
Have you ever looked into a pool of clear, still water and seen your own face? The surface of the water acts like a mirror and you can see your reflection. (In fact, before mirrors were invented, this was the only way people had to look at themselves.) If you were swimming below the surface, you’d still see your own face – the mirror effect works both ways.
Have you ever broken a pencil by sticking it into a glass of water? The pencil isn’t really broken, but it sure looks like it! What’s going on?
We’re going to bend light to make objects disappear. You’ll need two glass containers (one that fits inside the other), and the smaller one MUST be Pyrex. It’s okay if your Pyrex glass has markings on the side. Use cooking oil such as canola oil, olive oil, or others to see which makes yours truly disappear. You can also try mineral oil or Karo syrup, although these tend to be more sensitive to temperature and aren’t as evenly matched with the Pyrex as the first choices mentioned above.
Here’s what you need:
Published value for light speed is 299,792,458 m/s = 186,282 miles/second = 670,616,629 mph
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Hans Lippershey was the first to peek through his invention of the refractor telescope in 1608, followed closely by Galileo (although Galileo used his telescope for astronomy and Lippershey’s was used for military purposes). Their telescopes used both convex and concave lenses.
A few years later, Kepler swung into the field and added his own ideas: he used two convex lenses (just like the ones in a hand-held magnifier), and his design the one we still use today. We're going to make a simple microscope and telescope using two lenses, the same way Kepler did. Only our lenses today are much better quality than the ones he had back then!
You can tell a convex from a concave lens by running your fingers gently over the surface – do you feel a “bump” in the middle of your hand magnifying lens? You can also gently lay the edge of a business card (which is very straight and softer than a ruler) on the lens to see how it doesn't lay flat against the lens.
Your magnifier has a convex lens – meaning the glass (or plastic) is thicker in the center than around the edges. The image here shows how a convex lens can turn light to a new direction using refraction. You can read more about refraction here.
A microscope is very similar to the refractor telescope with one simple difference – where you place the focus point. Instead of bombarding you with words, let’s make a microscope right now so you can see for yourself how it all works together. Are you ready?
Spectrometers are used in chemistry and astronomy to measure light. In astronomy, we can find out about distant stars without ever traveling to them, because we can split the incoming light from the stars into their colors (or energies) and “read” what they are made up of (what gases they are burning) and thus determine their what they are made of. In this experiment, you’ll make a simple cardboard spectrometer that will be able to detect all kinds of interesting things!
SPECIAL NOTE: This instrument is NOT for looking at the sun. Do NOT look directly at the sun. But you can point the tube at a sheet of paper that has the sun’s reflected light on it.
Usually you need a specialized piece of material called a diffraction grating to make this instrument work, but instead of buying a fancy one, why not use one from around your house? Diffraction gratings are found in insect (including butterfly) wings, bird feathers, and plant leaves. While I don’t recommend using living things for this experiment, I do suggest using an old CD.
CDs are like a mirror with circular tracks that are very close together. The light is spread into a spectrum when it hits the tracks, and each color bends a little more than the last. To see the rainbow spectrum, you’ve got to adjust the CD and the position of your eye so the angles line up correctly (actually, the angles are perpendicular).
You’re looking for a spectrum (the rainbow image at left) – this is what you’ll see right on the CD itself. Depending on what you look at (neon signs, chandeliers, incandescent bulbs, fluorescent bulbs, Christmas lights…), you’ll see different colors of the rainbow. For more about how diffraction gratings work, click here.
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This is the simplest form of camera – no film, no batteries, and no moving parts that can break. The biggest problem with this camera is that the inlet hole is so tiny that it lets in such a small amount of light and makes a faint image. If you make the hole larger, you get a brighter image, but it’s much less focused. The more light rays coming through, the more they spread out the image out more and create a fuzzier picture. You’ll need to play with the size of the hole to get the best image.
While you can go crazy and take actual photos with this camera by sticking on a piece of undeveloped black and white film (use a moderately fast ASA rating), I recommend using tracing paper and a set of eyeballs to view your images. Here’s what you need to do:
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Here’s a trick question – can you make the color “yellow” with only red, green, and blue as your color palette? If you’re a scientist, it’s not a problem. But if you’re an artist, you’re in trouble already.
The key is that we would be mixing light, not paint. Mixing the three primary colors of light gives white light. If you took three light bulbs (red, green, and blue) and shined them on the ceiling, you’d see white. And if you could magically un-mix the white colors, you’d get the rainbow (which is exactly what prisms do.)
If you’re thinking yellow should be a primary color – it is a primary color, but only in the artist’s world. Yellow paint is a primary color for painters, but yellow light is actually made from red and green light. (Easy way to remember this: think of Christmas colors – red and green merge to make the yellow star on top of the tree.)
As a painter, you know that when you mix three cups of red, green, and blue paint, you get a muddy brown. But as a scientist, when you mix together three cups of cold light, you get white. If you pass a beam white light through a glass filled with water that’s been dyed red, you’ve now got red light coming out the other side. The glass of red water is your filter. But what happens when you try to mix the different colors together?
The cold light is giving off its own light through a chemical reaction called chemiluminescence, whereas the cups of paint are only reflecting nearby light. It’s like the difference between the sun (which gives off its own light) and the moon (which you see only when sunlight bounces off it to your eyeballs). You can read more about light in our Unit 9: Lesson 1 section.
Here’s what you need:
When you warm up leftovers, have you ever wondered why the microwave heats the food and not the plate? (Well, some plates, anyway.) It has to do with the way microwave ovens work.
Microwave ovens use dielectric heating (or high frequency heating) to heat your food. Basically, the microwave oven shoots light beams that are tuned to excite the water molecule. Foods that contain water will step up a notch in energy levels as heat. (The microwave radiation can also excite other polarized molecules in addition to the water molecule, which is why some plates also get hot.)
One of the biggest challenges with measuring the speed of light is that the photons move fast… too fast to watch with our eyeballs. So instead, we’re going to watch the effects of microwave light and base our measurements on the effects the light has on different kinds of food. Microwaves use light with a wavelength of 0.01 to 10 cm (that’s ‘microwave’ part of the electromagnetic spectrum). When designing your experiment, you’ll need to pay close attention to the finer details such as the frequency of your microwave oven (found inside the door), where you place your food inside the oven, and how long you leave it in for.
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Imagine you’re a painter. What three colors do you need to make up any color in the universe? (You should be thinking: red, yellow, and blue… and yes, you are right if you’re thinking that the real primary colors are cyan, magenta, and yellow, but some folks still prefer to think of the primary colors as red-yellow-blue… either way, it’s really not important to this experiment which primary set you choose.)
Here’s a trick question – can you make the color “yellow” with only red, green, and blue as your color palette? If you’re a scientist, it’s not a problem. But if you’re an artist, you’re in trouble already.
The key is that we would be mixing light, not paint. Mixing the three primary colors of light gives white light. If you took three light bulbs (red, green, and blue) and shined them on the ceiling, you’d see white. And if you could magically un-mix the white colors, you’d get the rainbow (which is exactly what prisms do.)
If you’re thinking yellow should be a primary color – it is a primary color, but only in the artist’s world. Yellow paint is a primary color for painters, but yellow light is actually made from red and green light. (Easy way to remember this: think of Christmas colors – red and green merge to make the yellow star on top of the tree.) It’s because you are using projection of light, not the subtrative combination of colors to get this result.
Here’s a nifty experiment that will really bring these ideas to life (and light!):
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When I was in grad school, I needed to use an optical bench to see invisible things. I was trying to ‘see’ the exhaust from a new kind of F15 engine, because the aircraft acting the way it shouldn’t – when the pilot turned the controls 20o left, the plane only went 10o. My team had traced the problem to an issue with the shock waves, and it was my job to figure out what the trouble was. (Anytime shock waves appear, there’s an energy loss.)
Since shock waves are invisible to the human eye, I had to find a way to make them visible so we could get a better look at what was going on. It was like trying to see the smoke generated by a candle – you know it’s there, but you just can’t see it. I wound up using a special type of photography called Schlieren.
An optical table gives you a solid surface to work on and nails down your parts so they don’t move. This is an image taken with Schlieren photography. This technique picks up the changes in air density (which is a measure of pressure and volume).
The air above a candle heats up and expands (increases volume), floating upwards as you see here. The Schlieren technique shines a super-bright xenon arc lamp beam of light through the candle area, bounces it off two parabolic mirrors and passes it through a razor-edge slit and a neutral density filter before reaching the camera lens. With so many parts, I needed space to bolt things down EXACTLY where I wanted them. The razor slit, for example, just couldn’t be anywhere along the beam – it had to be right at the exact point where the beam was focused down to a point.
I’m going to show you how to make a quick and easy optical lab bench to work with your lenses. Scientists use optical benches when they design microscopes, telescopes, and other optical equipment. You’ll need a bright light source like a flashlight or a sunny window, although this bench is so light and portable that you can move it to garage and use a car headlight if you really want to get creative. Once your bench is set up, you can easily switch out filters, lenses, and slits to find the best combination for your optical designs. Technically, our setup is called an optical rail, and the neat thing about it is that it comes with a handy measuring device so you can see where the focal points are for your lenses. Let’s get started:
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Charles Benhamho (1895) created a toy top painted with the pattern (images on next page). When you spin the disk, arcs of color (called “pattern induced flicker colors”) show up around the disk. And different people see different colors!
We can’t really say why this happens, but there are a few interesting theories. Your eyeball has two different ways of seeing light: cones and rods. Cones are used for color vision and for seeing bright light, and there are three types of cones (red, green, and blue). Rods are important for seeing in low light.
One possibility is… Please login or register to read the rest of this content.
In this experiment, water is our prism. A prism un-mixes light back into its original colors of red, green, and blue. You can make prisms out of glass, plastic, water, oil, or anything else you can think of that allows light to zip through.
What’s a prism? Think of a beam of light. It zooms fast on a straight path, until it hits something (like a water drop). As the light goes through the water drop, it changes speed (refraction). The speed change depends on the angle that the light hits the water, and what the drop is made of. (If it was a drop of mineral oil, the light would slow down a bit more.) Okay, so when white light passes through a prism (or water drop), changes speed, and turns colors. So why do we see a rainbow, not just one color coming out the other side?
In a simplest sense, a kaleidoscope is a tube lined with mirrors. Whether you leave the end opened or tape on a bag of beads is up to you, but the main idea is to provide enough of an optical illusion to wow your friends. Did you know that by changing the shape and size of the mirrors, you can make the illusion 3D?
If you use only two mirrors, you’ll get a solid background, but add a third mirror and tilt together into a triangle (as shown in the video) and you’ll get the entire field filled with the pattern. You can place transparent objects at the end (like marbles floating in water or mineral oil) or just leave it open and point at the night stars.
The first kaleidoscopes were constructed in 1816 by a scientist while studying polarization. They were quickly picked up as an amusement gadget by the public and have stayed with us ever since.
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There are three primary colors of light are red, green, and blue. The three primary colors of paint are red, yellow, and blue (I know it’s actually cyan, yellow, and magenta, which we’ll get to in more detail later, but for now just stick with me and think of the primary colors of paint as red-yellow-blue and I promise it will all make sense in the end).
Most kids understand how yellow paint and blue paint make green paint, but are totally stumped when red light and green light mix to make yellow light. The difference is that we’re mixing light, not paint.
Lots of science textbooks still have this experiment listed under how to mix light: “Stir together one of red water and one glass of green water (dyed with food coloring) to get a glass of yellow water.” Hmmm… the result I get is a yucky greenish-brown color. What happened?
The reason you can’t mix green and red water to get yellow is that you’re essentially still mixing paint, not light. But don’t take our word for it – test it out for yourself with this super-fast light experiment on mixing colors.
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Ever play with a prism? When sunlight strikes the prism, it gets split into a rainbow of colors. Prisms un-mix the light into its different wavelengths (which you see as different colors). Diffraction gratings are tiny prisms stacked together.
When light passes through a diffraction grating, it splits (diffracts) the light into several beams traveling at different directions. If you’ve ever seen the ‘iridescence’ of a soap bubble, an insect shell, or on a pearl, you’ve seen nature’s diffraction gratings.
Scientist use these things to split incoming light so they can figure out what fuels a distant star is burning. When hydrogen burns, it gives off light, but not in all the colors of the rainbow, only very specific colors in red and blue. It’s like hydrogen’s own personal fingerprint, or light signature.
Astronomers can split incoming light from a star using a spectrometer (you can build your own here) to figure out what the star is burning by matching up the different light signatures.
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Did you know that the word LASER stands for Light Amplification by Stimulated Emission of Radiation? And that a MASER is a laser beam with wavelengths in the microwave part of the spectrum? Most lasers fire a monochromatic (one color) narrow, focused beam of light, but more complex lasers emit a broad range of wavelengths at the same time.
In 1917, Einstein figured out the basic principles for the LASER and MASER by building on Max Planck’s work on light. It wasn’t until 1960, though when the first laser actually emitted light at Hughes Research Lab. Today, there are several different kinds of lasers, including gas lasers, chemical lasers, semiconductor lasers, and solid state lasers. One of the most powerful lasers ever conceived are gamma ray lasers (which can replace hundreds of lasers with only one) and the space-based x-ray lasers (which use the energy from a nuclear explosion) – neither of these have been built yet!
By using lenses and mirrors, you can bounce, shift, reflect, shatter, and split a laser beam. Since the laser beam is so narrow and focused, you’ll be able to see several reflections before it fades away from scatter. Make sure you complete the Laser Basics experiment first before working with this experiment.
You’ll need to make your beam visible for this experiment to really work. There are several different ways you can do this:
This is a super-cool and ultra-simple circuit experiment that shows you how a CdS (cadmium sulfide cell) works. A CdS cell is a special kind of resistor called a photoresistor, which is sensitive to light.
A resistor limits the amount of current (electricity) that flows through it, and since this one is light-sensitive, it will allow different amounts of current through depends on how much light it "sees".
Photoresistors are very inexpensive light detectors, and you'll find them in cameras, street lights, clock radios, robotics, and more. We're going to play with one and find out how to detect light using a simple series circuit.
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This is a super-cool and ultra-simple circuit experiment that shows you how a CdS (cadmium sulfide cell) works. A CdS cell is a special kind of resistor called a photoresistor, which is sensitive to light.
A resistor limits the amount of current (electricity) that flows through it, and since this one is light-sensitive, it will allow different amounts of current through depends on how much light it "sees".
Photoresistors are very inexpensive light detectors, and you'll find them in cameras, street lights, clock radios, robotics, and more. We're going to play with one and find out how to detect light using a simple series circuit.
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Ever notice how BRIGHT your white t-shirt looks in direct sun? That’s because mom washed with fluorescent laundry soap (no kidding!). The soap manufacturers put in dyes that glow white under a UV light, which make your clothes appear whiter than they really are.
Since light is a form of energy, in order for things to glow in the dark, you have to add energy first. So where does the energy come from? There are are few different ways to do this:
What happens when you shine a laser beam onto a spinning mirror? In the Laser Maze experiment, the mirrors stayed put. What happens if you took one of those mirrors and moved it really fast?
It turns out that a slightly off-set spinning mirror will make the laser dot on the wall spin in a circle. Or ellipse. Or oval. And the more mirrors you add, the more spiro-graph-looking your projected laser dot gets.
Why does it work? This experiment works because of imperfections: the mirrors are mounted off-center, the motors wobble, the shafts do not spin true, and a hundred other reasons why our mechanics and optics are not dead-on straight. And that’s exactly what we want – the wobbling mirrors and shaky motors make the pretty pictures on the wall! If everything were absolutely perfectly aligned, all you would see is a dot.
Here’s how to do this experiment:
This experiment is for advanced students.Did you know that when you talk inside a house, the windows vibrate very slightly from your voice? If you stand outside the house and aim a laser beam at the window, you can pick up the vibrations in the window and actually hear the conversation inside the house.
Remember how windows split a laser beam in two from the Laser Basics experiment? That’s the basic idea behind it. First, I’ll show you how to build your own space-age laser communicator, then you can work on your spy device.
The first thing we’re going to do is take the music from your stereo or MP3 player and transmit it on a laser beam to a detector on the other side. The detector has an earphone attached, so someone else can listen to the music from your laser. Weird, huh?
Here’s how to build your own:
So you’ve played with lenses, mirrors, and built an optical bench. Want to make a real telescope? In this experiment, you’ll build a Newtonian and a refractor telescope using your optical bench.
Materials:
Light can be either a wave or a particle, but not both at the same time. Which one it is will depend on what it’s doing. In this section, you’ll be able to figure out how intensity (how bright), frequency (wavelength), polarization (the direction of the electric field), and phase (time shift) all affect the kind of light you see and don’t see. Most light isn’t detectable by the human eye, which makes studying light more like investigating a crime scene. You’ll quickly be puzzling the pieces together to explain why pencils in a glass of water appear broken, why light beams can fry an egg, and how to build a telescope.
The word “LASER” stands for Light Amplification by Stimulated Emission of Radiation. A laser is an optical light source that emits a concentrated beam of photons. Lasers are usually monochromatic – the light that shoots out is usually one wavelength and color, and is in a narrow beam. By contrast, light from a regular incandescent light bulb covers the entire spectrum as well as scatters all over the room. (Which is good, because could you light up a room with a narrow beam of light?).
Soon you’ll be building shattering light rays, firing music on a laser beam, and building your own laser light show from tupperware. Let’s get started by learning about lasers with this video:
UV (ultra-violet) light is invisible, which means you need more than your naked eyeball to do experiments with it. Our sun gives off light in the UV. Too much exposure to the sun and you’ll get a sunburn from the UV rays.
There are many different experiments you can do with UV detecting materials, such as color-changing UV beads and UV nail polish.
Here are a few fun activities you can do with your UV detecting materials:
This stuff is definitely sci-fi weird, and probably not appropriate for younger grades (although we did have a seven year old reiterate in his own words this exact phenomenon to a physics professor, so hey… anything possible! Which is why we’ve included it here.)
This experiment is also known as Young’s Experiment, and it demonstrates how the photon (little packet of light) is both a particle and a wave, and you really can’t separate the two properties from each other. If the idea of a ‘photon’ is new to you, don’t worry – we’ll be covering light in an upcoming unit soon. Just think of it as tiny little packets or particles of light. I know the movie is a little goofy, but the physics is dead-on. Everything that “Captain Quantum” describes is really what occurred during the experiment. Here’s what happened:
So basically, any modification of the experiment setup actually determines which slit the electrons go through. This experiment was originally done with light, not electrons. and the interference pattern was completely destroyed (as shown in the end of the video) by an ‘observer’. This shows you that light can either be a wave or a particle, but not both at the same time, and it has the ability to flip between one and the other very quickly. (The image at the left is a photograph of an interference pattern – the same thing you’d see on the wall if you tried this experiment.)
So, both light and electrons have wave-particle characteristics. Now, take your brain this last final step… it’s easier to see how this could be true for light, you can imagine as a massless photon.
But an electron has mass. Which means that matter can act as a wave. Twilight zone, anyone?
Read more about this in our Advanced Physics Section.
This experiment is for advanced students. Radio astronomy is the study of radio waves originating outside the Earth. The radio range of frequencies or wavelengths is loosely defined by three factors: atmospheric transparency, current technology, and fundamental limitations imposed by quantum noise. Together they yield a boundary between radio and far-infrared astronomy at frequency 1 THz (1 THz =1012 Hz) or wavelength =0.3 mm.
If you’re an advanced high school-age student with a yearning to learn more about radio astronomy, you’re in the right place. First, you’ll get a college-level course about the fundamentals of radio astronomy with a full textbook, and you’ll also find problem sets with solutions and also a final exam.The lab included will have you building your very own radio telescope for under $100. Feel free to build the telescope as you work through the text or straight off the bat. If you’re allergic to math, just skip over those sections to get at the really interesting stuff. Click here to download the full text or use the links below.
When you warm up leftovers, have you ever wondered why the microwave heats the food and not the plate? (Well, some plates, anyway.) It has to do with the way microwaves work.
Microwaves generate high energy electromagnetic waves that when aimed at water molecules, makes these molecules get super-excited and start bouncing around a lot.
We see this happen when we heat water in a pot on the stove. When you add energy to the pot (by turning on the stove), the water molecules start vibrating and moving around faster and faster the more heat you add. Eventually, when the pot of water boils, the top layer of molecules are so excited they vibrate free and float up as steam.
When you add more energy to the water molecule, either by using your stove top or your nearest microwave, you cause those water molecules to vibrate faster. We detect these faster vibrations by measuring an increase in the temperature of the water molecules (or in the food containing water). Which is why it’s dangerous to heat anything not containing water in your microwave, as there’s nowhere for that energy to go, since the electromagnetic radiation is tuned to excite water molecules.
To explain this to younger kids (who might confuse radio waves with sounds waves) you might try this:
There’s light everywhere, some of which you can see (like rainbows) and others that you can’t see (like the infrared beam coming from your TV remote, or the UV rays from the sun that give you a sunburn). The microwave shoots invisible light beams at your food that are tuned to heat up the water molecule.
The microwave radiation emitted by the microwave oven can also excite other polarized molecules in addition to the water molecule, which is why some plates also get hot. The soap in this experiment below will show you how a bar of Ivory soap contains air, and that air contains water vapor which will get heated by the microwave radiation and expand. Are you ready?
Here’s what you need:
