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.

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!) :)

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