Holograms

This is a great site, but overwhelming because there is just so much information to get through! His diagrams are really clear, though, and it would be really cool to make your own holograms as he describes.

Probably the best of these videos on how holograms are made.

Good explanation of holograms, and why "3-D" movies don't actually give you the same type of experience—but maybe they could someday!

Maybe like this: here is a demonstration of some new technology that can project text and images in mid-air. It works by ionizing the molecules in the air to make them light up.

Another video of the same technology.

This isn't actually using holograms, but digital projection that makes things look they are present in 3-D through optical illusion and angled screens. I think these images are often called holographic.

Making a Laser Projection Microscope

We learned about this awesome project from The Happy Scientist (subscription required for this video). He gave a great, simple explanation about what to do, and we had no trouble getting it to work. And it was so cool! You can probably find other tutorials for this project online, also. (Yes. Here is one.)

Basically, what you're doing is creating a little loop in which a drop of water can be suspended by surface tension. The water acts like a lens for the laser light to shine through. The light is then projected onto a screen and, voila!, you can see tiny little microorganisms in the water. It is amazing. We used pond water to make sure there would be lots of life in it, and there was! We saw all types of different protazoa, flagellates, etc., with all types of movement going on. Some things zipped across the screen quickly, some sort of lurched along, others were definitely swimming. So cool! This is one of the most impressive activities we did this entire unit, and the children LOVED it. They wanted to show it to everyone who came to our house for the next several days.

It's hard to see anything very clearly in the picture above, but this video is really cool. You can see several organisms moving around in the drop of water, and observe the different ways they move. You should definitely try this project yourself!

Lasers

I can't even describe to you how much the children delight in saying "light amplification through stimulated emission of radiation." They think they're so funny. And we loved learning about lasers! They are cool.

This is the laser pointer we have. We really like it.

Here's a good, simple explanation with pictures of how lasers work and what they are.

Lots of good videos about lasers here.

This video was okay—better in conjunction with the others, though, as we didn't think it explained the process very clearly.

This video has no narration, but just text. We liked it because it described semiconductor lasers, which are slightly different than the solid state, gas, dye, or other lasers. (We learned about semiconductors earlier, during our electricity unit, and our favorite video then was this one.)

This one is less about the lasers themselves, but more about laser cutters. Still interesting though.

This was interesting because it showed an open cavity laser, which makes it easy to see what is going on. This is a helium-neon laser.

Very clear and well-explained. Shows why a ruby is often used in a solid-state laser. This video really helped us realize why "pumping" is needed before the laser actually starts working (something we didn't understand before).

Just screens of text. But a good analogy.

Another video that is quite clear about how stimulated emission of radiation is created. Good animations (except the one of Einstein!) :)

Light in Art; Pointillism

It would be a shame to talk about only the science of light and not the importance of light in art, especially with our resident expert to help us out. We actually didn't have as much input from Sam as we would have liked, as the days we studied art and light corresponded with a very busy few days for him, but we had some good books and we really liked the things we did learn.

My favorite book was this one, which talked about how different time periods and artistic movements affected the way artists captured light in their work. It had great examples from a variety of art styles.

We talked a lot about the Impressionist Movement because of those artists' intense focus on capturing light in a scene. Here's a good video we watched about Monet, and we also found several books on him, and other Impressionist artists, at the library.

We also covered Georges Seurat and Pointillism. I found lots of ideas online for art projects related to Pointillism, but for this unit on light we wanted to focus more on subtractive color mixing and the way your eyes mix the separate points of color to create other colors, so we talked mostly about that. Then we made Pointillist pictures with markers (since I felt like adding the actual mixing of paints to this project would just obscure the ideas we were trying to focus on).

I really loved the pictures the children came up with. One of my favorite things was this line of rainbow colors Sebby made, on the bottom right below:

You can see the six boxes with definite colors: pink, orange, yellow, green, blue, purple.

But when you look at them up close, they are just mixed dots of primary colors! So interesting!

Abe's bear

I loved Junie's picture. You can't see all the tiny dots she made, but there are hundreds of them. She worked so hard on this!

I really loved Daisy's ice cream cone (with matching tiny ice cream cone) too.

And we only ruined a few markers! :)

Fiber Optics

We spent a day talking about fiber optics. I knew they used fiber optic cables for transmitting phone and internet signals, but my only real association with fiber optics was a color-changing lamp someone gave our family when I was little, like this:

which I assumed was not really "fiber optic" at all.

But the actual concept, of how light can travel through a flexible glass tube and come out at the end, really is about the same. Here is a demonstration of how light is bent to the "critical angle" so it won't escape the fiber optic cable.

Here's a video on how fiber optic cables are made

Another video on how the cables are made—this one is more technical, but it was still interesting to skim through

We really liked this explanation, and it includes a demonstration you can do yourself with an old plastic bottle.

Another explanation that includes a diagram of the parts of a fiber optic cable.

Some discussion of why fiber optic can be faster than regular copper wire.

Making marbled paper

I've seen this project cited as a good way to demonstrate the different densities of different materials, but we used it when we were talking about color printing in books. This process, where the oil sticks to certain areas of the paper and not to others, is a lot like the way certain colors and dyes are transferred to the page when books and magazines are printed.

I don't know if we did it exactly right—our paper looked very pretty but not nearly like the papers she shows in this tutorial! Still, we had a fun time.

And here's another tutorial here, in case you don't have oil paints to use (we didn't).

Atmospheric lighting effects

We had this book from the library, and we liked it so much that I got it for Sam for Christmas. We love observing/remarking on stuff like this, so it is nice to learn more about HOW and WHY these effects occur!

This video shows the "green flash", which is an interesting phenomenon I'd heard of, but never really understood, before. The book pictured above had a pretty good explanation of why it occurs, to which I doubt I can do justice. But here's a web page about it if you're interested, or this one is a bit simpler. Just like practically everything we learned about in this unit, it seems confusing, then simpler when you first hear it explained, then even more confusing and mysterious the more in-depth the explanation becomes! :)

Here's another video that shows a photographer trying to capture the green flash.

Some other phenomena I've always been interested in are the aurora. I (like everyone else in the world, I suppose) have always dreamed of seeing them for myself someday!
There are some great pictures of the aurora borealis here
And more beautiful pictures here
And this video gives you an idea of how beautiful it must be to see the aurora in real-time!

Prisms, Rainbows, Light Scattering

We liked creating a prism with a mirror, light, and water (something similar is described here) and projecting the spectrum on the wall. So pretty!

Apparatus: water in pan, angled mirror, flashlight

We mixed three colored lights to make white light (additive)

Color mixing (subtractive)

"Daylight"

"Sunset light"

We learned about Tyndall Scattering in the atmosphere—that's the effect that makes the sky appear blue when the light is coming from overhead, and reddish when the light is coming at a sideways angle. A similar demonstration is described here.

Another brilliant spectrum on the wall, from a glass prism this time. It's so fun to play with prisms—I remember doing it for hours at a time when I was little.

Making a pinhole camera

Making a pinhole camera is one of those things that feels like kind of an obligatory part of learning about light. I feel like I did it several times when I was young. And, true, it is an interesting way to discover how images are turned upside-down when coming through a thin opening (as on the retina of your eye). But I must say it's not one of my favorite activities, just because it's so…underwhelming. The images you see inside the camera are so small and blurry and faded! But, it's an easy-enough activity to do, so maybe it's worth it anyway. Or maybe there is a model that works better than the one we made. We got our instructions from a library book, but here are some online instructions for how to make a pinhole camera from a Pringles can.

Here's another version.

Or you could make a pinhole camera that actually records pictures onto film? That sounds kind of cool.

Telescopes

We got a telescope through a charter school program last year, but we still had it in the box, so during this unit after we talked about lenses seemed like the perfect time to finally get it out and put it together. It's this telescope, and we haven't used it much for stars yet, but we did have fun learning how it worked and experimenting with looking at signs and trees and things.

Poor Daisy got tired of waiting for her turn. Seems like she always has to wait for the older children!

(Our cousin Michael was visiting, too)

The innovations that have been made in telescopes and lenses in the last several years are just amazing. We read lots of books about some of the new space telescopes, and we always love looking at pictures from the Hubble Space Telescope!

We learned about liquid mirror telescopes made of mercury, which I had never heard of. Apparently these liquid mirrors are a lot cheaper to make than the huge, flawless mirrors they need to grind for other telescopes (and which can take years to get smooth enough). But the liquid mirrors have a few problems too (e.g. they can't be tilted).

This video of a spinning parabolic mercury mirror demonstrates how it works on a small scale.

Lenses

Resources for learning about lenses:

How lenses for glasses are made

Fascinating page on the Fresnel Lens (used in lighthouses) and we also loved this video showing how they work. Such an ingenious concept!

Here are some lenses we used for experimentation.

While discussing lenses, we used both our microscope (we have this one, which we got a couple years ago and have really loved) and our telescope (this one, which is quite new and we have hardly used it, so I can't say if it's a good one or not. The reviews say it's good for beginners, which we definitely are).

This is a great discussion of why things in a microscope get darker as the magnification increases (and why there is a limit to what we can see with optical microscopes!)

This page tells how lenses are used to make searchlights and car headlights brighter.

We liked these diagrams showing how different lenses can work together in a lens array. Since Sebastian is currently obsessed with digital cameras and how they work, this was particularly interesting to him, as was this page on SLR cameras. There's a cool interactive feature on that page where you can change ISO, aperture, shutter speed, etc. and see how those changes affect the photograph.

Refraction

Sam taught some of the lessons on refraction since he knows a lot more about it than I do! He may have gotten a little carried away when discussing how to calculate angles of refraction, but even if we didn't get it all, we learned a lot! :)

Sam had the children roll toy cars (photons) in a straight line on the hard floor and see what happened when they reached a different material (the carpet). It was a great demonstration of how light changes speed (and often, direction) as it passes through different media.

Refraction at work: you can see the house outside refracted upside-down in the curved water glass!

We saw how even a curved water-drop can act like a lens, to refract light and magnify what is beneath it.

We saw how chromatic aberration can occur as light refracts and separates just slightly into its different wavelengths.

A laser's light being refracted through water

These lenses were great for experimenting with refraction, and how different shapes cause light to refract at different angles.

Sebastian even found an incident angle that made nearly all of the light refract and reflect inside the glass, back out of the other end of the lens! I think something similar to this is occurring inside a fiberoptic cable to keep the light inside the cable as it goes around curves and corners.

If you don't have lenses and lasers to use, you can download this angle of refraction simulator to experiment with how light bends through different objects. I think there are mathematical ways to figure this out for yourself, but I don't know them! It was interesting to see how different materials affected the refraction of the light.

Here's a video that discusses these concepts. It gets a bit technical in parts, but we liked the animations (and the narrator has a great accent!) :)

Mirrors and Reflection; Make a periscope; Make a one-way mirror

There is so much to learn about mirrors and reflection! We really liked making this periscope for an activity. (You can find instructions for a similar periscope here.) We wished it could have been even longer, but longer periscopes make the image you see even smaller, so maybe it wouldn't have been as cool as we thought.

More resources on reflection: 

Video about How mirrors are made

Another (sort of silly) video on how mirrors work

(As I mention on the telescope post, the videos here on how liquid mercury mirrors are made are very interesting also.)

This page talks about different types of reflection (specular vs diffuse)

This page is great—lots of good diagrams, explanation of what is happening in convex vs. concave mirrors, why mirrors reverse what we see, etc.

The children were always asking about how the auto-dimming rearview mirror in our car worked, and I had wondered a lot about it myself! We found a couple sites that explain it well: here and here.

We also talked about one-way (or is it two-way?) mirrors. The kind that look like a mirror on one side, but you can see through them like glass on the other side. :) 

This site gives a good explanation of how they work, as does this one. The basic idea is that you need a very, very thin film of reflective material—so thin that with a strong light on one side, you can see through it, but without that back light, it reflects light like a mirror would.

Knowing this, you can make your own fairly easily. We got it to work, though not perfectly. We took a clear piece of glass from a picture frame and covered it with thin Mylar sheets (something like this) on one side. It worked just like a mirror when the lighting on both sides of it was consistent. Thus you can see me in the mirror, taking a picture with the camera. (left side, above)

However, when we dimmed the lights on one side, and turned on a bright lamp on the other side, the "mirror" became more of a "window," and I could see Abraham looking at me through it (right side, above).

Polarization of light

Polarization is one of those things I assumed I understood but I really didn't. Sam is always going on and on about it (every time he wears his sunglasses he notices some new effect to make observations about) but now I finally, at least somewhat, understand what is making these effects occur! 

We watched this Happy Scientist video, and then this one, which gave great explanations of what is happening when light is polarized. He describes the phenomenon of birefringence (which is what we're seeing in that CD case pictured above—the photograph was taken through our polarizing filter) and shows how you can use two polarizing films together to twist the light back so you can see through it again! Like this:

Polarized sunglasses: at this angle they are darkening the computer's LCD screen slightly, but not blocking all the light, because they aren't turned in the same direction the (already-polarized) light from the screen is coming from.

When we turn the glasses, they now block all the polarized light from the screen.

But, if I hold another polarizing film up behind the glasses and twist it at an angle halfway between the others, it actually undarkens (??) the screen, and makes a window we can see through! So cool!

A few more good links: 

A video about polarization filters

A video about the difference between circular and linear polarization

This experiment shows how you can change the direction of polarization in light

A website entirely about polarization

Interference effects and light

Any discussion of wave-particle duality has to include the famous two-slit experiment! This is one that's pretty easy to replicate at home (well, part of it, anyway) and it's cool to see the interference pattern demonstrating the wave property of light!

There are several good ways to do this demonstration: this one here is clear and easy to follow.

You can also look at diffraction patterns using these instructions here.

Light viewed through a diffraction grating

For a clear visual demonstration of how interference effects make patterns, you can use these printable moiré patterns. I love moiré patterns—my dad had a whole book of them where you moved one film on top of another to create those strange moving shapes. They can be very beautiful and elaborate. The idea is really the same as the interference you get with waves of light: two superimposed peaks create darker patches, a peak and a trough superimposed cancel each other out. A good explanation is here. 

To make these moiré patterns, I just printed off several pdf files from this site onto transparency film (this kind worked great for my printer). When you move and rotate the different patterns on top of each other, you get various beautiful moiré effects.

Here's a short video of how the patterns change as you move them around. So pretty!

We also talked about thin-film interference, or iridescence. This page has a good explanation of why iridescence occurs in soap bubbles, peacock feathers, etc., and this article discusses the same effect.