What happens if you bring an object from far away up close to a lens? How does the image change? The answer is that it depends on what type of lens and the distance it is from the lens.
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Imagine you were designing a pair of eyeglasses. How would you know what kind of lens to make? How curved would it be? What would the magnification be? Here’s how you use the lens maker’s equation to figure out the critical information about a lens.
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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:
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Click here to go to next lesson on Line of Sight
The eye is a complex structure that detects and focuses light. Light first enters the eye through the cornea, a clear protective layer on the outside of the eye. The pupil, a black opening in the eye, lets light in. In dark rooms, the pupil will become larger, or dilate, in order to let in more light. If the room suddenly becomes bright, the pupil will become smaller. The pupil is surrounded by the brown, blue, grey, or green iris.
After passing through the pupil, light goes to the lens which, like a hand lens, is a clear curved structure that helps focus light on the retina, in the back of the eye. The retina is where the rods and cones are found.
This video is an old instructional film shown to pre-med students in the early 50s you might enjoy watching:
Click here to go to next lesson on Eye Balloon
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In this lab, we are going to make an eyeball model using a balloon. This experiment should give you a better idea of how your eyes work. The way your brain actually sees things is still a mystery, but using the balloon we can get a good working model of how light gets to your brain.
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Click here to go to next lesson on Nearsightedness and Farsightedness
The lens in the eye changes shape to bring objects into focus. Myopia (nearsightedness) is the lens’ inability to bring objects that are far away into focus. The light gets brought into focus in front of the retina, so the eyeglasses needed to correct for this have diverging lenses.
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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.
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Click here to go to next lesson on Specular and Diffuse Reflection
The law of reflection holds true no matter what angle the light hits the surface with. Specular reflection occurs when light reflects off smooth surfaces like mirrors or quiet lakes, and diffuse reflection happens when light reflects off rough surfaces (like everything else). How the light reflects off and scatters depends on the roughness of the material.
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Mirrors are used to gather light and create images, like the mirror in your bathroom or those found in telescopes. We’re going to actually make a telescope a little later, but now we need to learn how the mirror makes an image in the first place.
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Have you ever seen a candle in a mirror? The image of the candle looks like the reflected rays seem to be coming from the image point, but they really don’t. This type of image is a virtual images, because it appears that light is coming from this location, but it’s not really the case.
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Ray tracing is how scientists figure out the path that light takes by looking at the speed of the wave, the optical density of the medium, and how reflective the surface is. Ray tracing shows how light can reflect, bend, change direction as it moves from one medium to another. Let’s find out how you can locate any image of any point by tracing rays.
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Right angle mirrors are two mirrors that are connected together to form an L-shape. What’s interesting about this is that while normally you’d have one image appear in one mirror, you can have three images appear when you put them together at right angles! Here’s how…
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Your optic nerve can be thought of as a data cord that is plugged in to each eye and connects them to your brain. The area where the nerve connects to the back of your eye creates a blind spot. There are no receptors in this area at all and if something is in that area, you won’t be able to see it. This experiment locates your blind spot.
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Click here to go to next lesson on The Lens of the Eye
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.
You already are familiar with what happens to an image on a plane mirror. What if the mirror is curved? Spherical mirrors are mirrors that are like a small section of a ball. (You could also argue that a plane mirror is a spherical mirror with an infinitely large radius, but let’s save that for another time…)
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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.
Materials:
- sunlight
- dead leaf
- magnifying glass
- fire extinguisher
- adult help
Here’s what you need to do:
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Click here to go to next lesson on How Concave Mirrors Create Images
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:
- optical bench
- index card or white wall
- two double-convex lenses
- concave mirror
- popsicle stick
- mirror
- paper clip
- flash light
- black garbage bag
- scissors or razor
- rubber band
- wax paper
- hot glue
Click here to go to next lesson on Reflection Rules for Curved Mirrors
In concave mirrors, the incident parallel light traveling parallel to the principal axis passes through the focal point when it reflects. Conversely, incident parallel light traveling through the focal point will then travel parallel when it reflects.
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Reflection on a concave mirror uses two important basic rules: first, incident light traveling parallel to the principal axis passes through the focal point after it reflects on the surface. Second, incident light traveling through the focal point will travel parallel to the principle axis after it reflects.
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Spherical mirrors have aberration, which is a loss in the definition of the image because of the geometry of the mirror itself. It’s a defect in the mirror shape itself, which is caused by not being able to focus all the light to a specific point.
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Energy can take one of two forms: matter and light (called electromagnetic radiation). Light is energy that can travel through space. When you feel the warmth of the sun on your arm, that’s energy from the sun that traveled through space as infrared radiation (heat). When you see a tree or a bird, that’s light from the sun that traveled as visible light (red, orange… the whole rainbow) reflecting and bouncing off objects to get to your eye. Light can travel through objects sometimes… like the glass in a window.
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You can see objects because light from that object travels to your eyes. Sometimes light is reflected off objects before it reaches our eyes, and sometimes it comes straight from the source itself.
A candle is a light source. So is a campfire, a light bulb, and the sun. An apple, however, reflects light. It doesn’t give off any light on its own but you can see it because light waves bounce off the apple into your eye. If you shut off the light, then you can’t see the apple. In this same way, the sun is a light source, and the moon is a light reflector.
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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.
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Diffraction happens when light goes around obstacles in its path. Sound waves diffract bend around obstacles, so if you’re stuck behind a pillar at a concert, you can still hear just fine.
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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.
Materials:
- feather
- old CD or DVD
Here’s what you do: Take a feather and put it over an eye. Stare at a light bulb or a lit candle. You should see two or three flames and a rainbow X. Shine a flashlight on a CD and watch for rainbows. (Hint – the tiny “hairs” on the feather are acting like tiny prisms… take your homemade microscope to look at more of the feather in greater detail and see the tiny prisms for yourself!
What happens when you aim a laser through a diffraction grating? Here’s what you do:
Materials:
- laser pointer
- diffraction grating (you can use an old CD also)
Download Student Worksheet & Excercises
Exercises
- Which light source gave the most interesting results?
- What happens when you aim a laser beam through the diffraction grating?
- How is a CD different and the same as a diffraction grating?
- Why does the feather work?
Click here to go to next lesson on Useful Diffraction
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.)
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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.
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Click here to go to next lesson on Light Interference
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.
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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.
Materials:
- two pairs of polarized sunglasses
- tape (the 3/4″ glossy clear kind works best – watch second video below)
- window
Click here to go to next lesson on Shadows
The electromagnetic spectrum shows the different energies of light and how the energy relates to different frequencies. The wavelength (λ) equals the speed of light (c) divided by the frequency (ν), or λ = c / ν. The speed of light is: c = 3 x 108 m/s (300,000,000 meters per second).
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Do you see where the “visible light” rainbow section is in the electromagnetic spectrum image below? This small area shows the light that you can actually see with your eyeballs. Note that the “rainbow of colors” that make up our entire visible world only make up a small part of all the light, from 400-700 nm (nanometers, or 10-9.
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You can demonstrate the primary colors of light using glow sticks! When red, green, and blue cold light are mixed, you get white light. Simply activate the light stick (bend it until you hear a *crack* – that’s the little glass capsule inside breaking) and while wearing gloves, carefully slice off one end of the tube with strong cutters, being careful not to splash (do this over a sink).
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Is white or black a color? No and no. White is the mixture of all the colors (red, orange, yellow, green, blue indigo, and violet), so technically white isn’t a color of light but rather the combination of colors. Black is also not technically a color. In outer space, it’s pitch-black dark because there’s no light. In a room with the lights off, it’s also black. Black is the absence of color.
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When you change the wavelength, you change the color of the light. 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?
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Your eyes have two different light receptors located on the back of the eyeball. These are the rods, which see black, white and grays can detect different intensities. The cones can detect color when the light strikes the cells that have a color-sensing chemical reaction that gets activated and sends a pulse to the brain. There are three cones: red, which can detect red wavelengths and some orange and yellow, green cones (which can also detect blue and yellow) are the most sensitive to light, and blue cones.
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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.
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Click here to go to next lesson on Martian Sunsets
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.
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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.
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Click here to go to next lesson on Path Difference
Imagine you have a coherent light in a shoebox, and you cut two narrow slits out the side and shine the light on the far wall. The distance from one slit to the wall isn’t going to be exactly the same as the other, so there’s a “path difference”.
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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.
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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…
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To show how light acts like a wave, you can pass light through a glass of water and watch the rainbow reflections on the wall. Why does this happen? We’ve already covered this in a previous lesson, but basically when the light passes through the glass and the water, it bends to give different frequencies of light and therefore different colors.
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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!
Sound is a form of energy, and is caused by something vibrating. So what is moving to make sound energy?
Molecules. Molecules are vibrating back and forth at fairly high rates of speed, creating waves. Energy moves from place to place by waves. Sound energy moves by longitudinal waves (the waves that are like a slinky). The molecules vibrate back and forth, crashing into the molecules next to them, causing them to vibrate, and so on and so forth. All sounds come from vibrations.
Materials:
- 1 tongue-depressor size popsicle stick
- Three 3″ x 1/4″ rubber bands
- 2 index cards
- 3 feet of string (or yarn)
- scissors
- tape or hot glue
Click here to go to next lesson on Pressure Waves.
A sound wave is different from a light wave in that a sound is a mechanical wave, which requires particle interaction in order to exist. Light waves can travel in the vacuum of space, and we’ll talk more about this in our next section when we get to light.
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Think of your ears as ‘sound antennas’. There’s a reason you have TWO of these – and that’s what this experiment is all about. You can use any noise maker (an electronic timer with a high pitched beep works very well), a partner, a blindfold (not necessary but more fun if you have one handy), and earplugs (or use your fingers to close the little flap over your ear – don’t stick your fingers IN your ears!).
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Click here to go to next lesson on Speed of Sound.
Sound is a type of energy, and energy moves by waves. So sound moves from one place to another by waves; longitudinal waves to be more specific. So, how fast do sound waves travel? Well, that’s a bit of a tricky question. The speed of the wave depends on what kind of stuff the wave is moving through. The more dense (thicker) the material, the faster sound can travel through it.
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When something vibrates, it pushes particles. These pushed particles create a longitudinal wave. If the longitudinal wave has the right frequency and enough energy, your ear drum antennas will pick it up and your brain will turn the energy into what we call sound. The higher the amplitude, the more energy the wave has. Intensity of a measure of a wave’s power per unit area, and is measured in Watts per square meter.
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It may seem like walking across a balance beam and listening to your favorite song are very different activities, but they both depend on your ears. Ears are the sense organs that control hearing, which is the ability to detect sound. Ears also sense the position of the body and help maintain balance when you walk a balance beam or ride a bike.
Imagine a pebble being dropped into a lake. Waves of water go off in all directions. A similar thing happens when a car driving down the street honks its own. Waves go off from the car in all direction. The difference is that these are not waves of water, but instead are sound waves, which travel through the air. If you are nearby, some of those sound waves make it to your ear.
Here’s a video that shows you how everything works together so you can hear:
The pinna, or outer ear, which is the part of your ear that you can see, gathers up some of the sound waves, sends them down the ear canal, and eventually they strike the eardrum. The eardrum is a thin membrane that vibrates like a drum when the waves hit it. The vibrations pass three tiny bones, called the hammer, anvil, and stirrup, as well as a membrane called the oval window, causing them all to vibrate.
From the oval window, the vibrations go to the cochlea, liquid-filled space lined with hairs. The vibrations make waves in the cochlea’s liquid, just like waves in a pond, causing the hairs to move. The movement of the hairs sends a nerve impulse through the auditory nerve to the brain. The brain interprets the message and “tells” you what you have heard.
This video is an old instructional film shown to pre-med students in the early 50s you might enjoy watching:
Along with hearing, the ears play a major role in balance. Inside the ears are semicircular canals which are lined with hairs and full of liquid. When the body moves in one direction, the liquid in the semicircular canals move, causing the hairs to move. This sends a message to your brain, which gives instructions for the body’s muscles to contract or relax. This keeps you balanced.
There’s a cool video of a camera going inside the ear… watch out for the wax!
Click here to go to next lesson on Big Ears.
How do you think animals know we’re around long before they see us? Sure, most have a powerful sense of smell, but they can also hear us first. In this activity, we are going to simulate enhanced tympanic membranes (or ear drums) by attaching styrofoam cups to your ears. This will increase the number of sound waves your ears are able to capture.
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Click here to go to next lesson on Elasticity and Inertia.
Have you ever been in a thunders storm? Here’s how you can use wave speed to figure out how far away that lightning strike really was.
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Sound can change according to the speed at which it travels. Another word for sound speed is pitch. When the sound speed slows, the pitch lowers. With clarinet reeds, it’s high. Guitar strings can do both, as they are adjustable. If you look carefully, you can actually see the low pitch strings vibrate back and forth, but the high pitch strings move so quickly it’s hard to see. But you can detect the effects of both with your ears.