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Expert (My Uncle John- Major in Physics and is an Astrophysicist. VERY SMART MAN) 

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Expert (My Uncle John- Major in Physics and is an Astrophysicist. VERY SMART MAN) 

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Index refraction of water is different of that of air. Refraction is the bending of light. Light going through water is at a different velocity than that going through air. That difference is reflected in the index of refraction. Because the light slows down, it goes in hits the arrow and then comes back out. Index of refraction measures how fast light goes through the material.
If you have a pencil on it's own, you see it normally as a straight line. the time it takes for a light to bounce of the pencil is linear. When the light goes into a slower medium (water), then the light takes longer to go in the water and back to the eyes.

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NGSS defined natural phenomena as: Natural phenomena are observable events that occur in the universe and that we can use our science. knowledge to explain or predict. This is a phenomena because it meets those requirements. The reversal of the arrow is something that we can observe, and it can be explained through the scientific principles of light refractions.

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Looking through water is applicable to Louisiana because there is a state standard that applies to it. Also we have lots of water in Louisiana (rivers, ponds, lakes, swamps, bayous)that cause light refraction with cause not only this phenomena but also rainbows. The conversation of light refraction can then lead into prisms and rainbows.

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This phenomena is unique because it is a phenomena that can use in an experiment with students. It can also be adjusted to become the crooked pencil phenomena.

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Looking through water is a phenomena that has to do with light refraction causing the look of an image behind the water to be reversed.

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Grade Level: 4th grade
Standard: 4-PS4-2;  Develop a model to describe that light reflecting from objects and entering the eye allows objects to be seen.

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If you shine a beam of light (a bundle of parallel rays) through the air, it will travel in a straight line. Rays of light usually travel in straight lines until they hit something.

If a ray of light hits the surface of a sheet of glass, some light will be reflected by the surface of the glass. However, much of the light will pass through the glass, because glass is transparent.

Water affects light rays in a similar way. Some light will be reflected off the surface of the water, but much of the light will pass through the transparent water.

When a ray passes from air into glass the direction in which the light ray is travelling changes. The light ray appears to bend as it as it passes through the surface of the glass.

When a light ray passes from air into water a similar thing occurs: the light ray is bent as it strikes the surface of the water.

This 'bending of a ray of light' when it passes from one substance into another substance is called refraction.

The bending of a ray of light also occurs when the ray comes out of glass or water and passes into air.

Glass and water are thicker and heavier than air. They are said to be 'denser' than air.

What happens is that light slows down when it passes from the less dense air into the denser glass or water.

This slowing down of the ray of light also causes the ray of light to change direction. It is the change in the speed of the light that causes refraction.

This is a bit like when a car goes partly off the road and some of the wheels go into the softer edge of the road. The softer surface drags on the wheels and slows them down. This can cause the car to pull to the left, slightly changing its direction.

Direction of bending

When a ray of light passes from a less dense material (eg air) into a denser material (eg glass or water) it is bent away from the surface between the two materials. This means that in this situation the angle of refraction is always less than the angle of incidence.

However, if the ray of light hits the surface at right angles (ie at 90°) to the surface, the ray is not bent.

When a ray of light passes from a denser material (eg water or glass) into a less dense material (eg air) it is bent towards the surface between the two materials. This means that in this situation the angle of refraction is always greater than the angle of incidence.

You can apply these rules for the refraction of light to any prism, triangular or rectangular. They also apply to light passing through lenses.

The bending of a ray of light also occurs when light passes into and out of a glass lens.

© Commonwealth of Australia, 2003

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If you shine a beam of light (a bundle of parallel rays) through the air, it will travel in a straight line. Rays of light usually travel in straight lines until they hit something. If a ray of light hits the surface of a sheet of glass, some light will be reflected by the surface of the glass.

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Refraction is the bending of light (it also happens with sound, water and other waves) as it passes from one transparent substance into another.

This bending by refraction makes it possible for us to have lenses, magnifying glasses, prisms and rainbows. Even our eyes depend upon this bending of light. Without refraction, we wouldn't be able to focus light onto our retina.

Change of speed causes change of direction

Light refracts whenever it travels at an angle into a substance with a different refractive index (optical density).

This change of direction is caused by a change in speed. For example, when light travels from air into water, it slows down, causing it to continue to travel at a different angle or direction.

How much does light bend?

The amount of bending depends on two things:

Change in speed - if a substance causes the light to speed up or slow down more, it will refract (bend) more.

Angle of the incident ray - if the light is entering the substance at a greater angle, the amount of refraction will also be more noticeable. On the other hand, if the light is entering the new substance from straight on (at 90° to the surface), the light will still slow down, but it won't change direction at all.

Refractive index of some transparent substances

All angles are measured from an imaginary line drawn at 90° to the surface of the two substances This line is drawn as a dotted line and is called the normal.

If light enters any substance with a higher refractive index (such as from air into glass) it slows down. The light bends towards the normal line.

If light travels enters into a substance with a lower refractive index (such as from water into air) it speeds up. The light bends away from the normal line.

A higher refractive index shows that light will slow down and change direction more as it enters the substance.

Lenses

A lens is simply a curved block of glass or plastic. There are two kinds of lens.

A biconvex lens is thicker at the middle than it is at the edges. This is the kind of lens used for a magnifying glass. Parallel rays of light can be focused in to a focal point. A biconvex lens is called a converging lens.

A biconcave lens curves is thinner at the middle than it is at the edges. Light rays refract outwards (spread apart) as they enter the lens and again as they leave.

Refraction can create a spectrum

Isaac Newton performed a famous experiment using a triangular block of glass called a prism. He used sunlight shining in through his window to create a spectrum of colours on the opposite side of his room.

This experiment showed that white light is actually made of all the colours of the rainbow. These seven colours are remembered by the acronym ROY G BIV - red, orange, yellow, green, blue, indigo and violet.

Newton showed that each of these colours cannot be turned into other colours. He also showed that they can be recombined to make white light again.

The explanation for the colours separating out is that the light is made of waves. Red light has a longer wavelength than violet light. The refractive index for red light in glass is slightly different than for violet light. Violet light slows down even more than red light, so it is refracted at a slightly greater angle.

The refractive index of red light in glass is 1.513. The refractive index of violet light is 1.532. This slight difference is enough for the shorter wavelengths of light to be refracted more.

Rainbows

A rainbow is caused because each colour refracts at slightly different angles as it enters, reflects off the inside and then leaves each tiny drop of rain.

A rainbow is easy to create using a spray bottle and the sunshine. The centre of the circle of the rainbow will always be the shadow of your head on the ground.

The secondary rainbow that can sometimes be seen is caused by each ray of light reflecting twice on the inside of each droplet before it leaves. This second reflection causes the colours on the secondary rainbow to be reversed. Red is at the top for the primary rainbow, but in the secondary rainbow, red is at the bottom.

Activity ideas

Useful links

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Refraction is the bending of light (it also happens with sound, water and other waves) as it passes from one transparent substance into another. This bending by refraction makes it possible for us to have lenses, magnifying glasses, prisms and rainbows. Even our eyes depend upon this bending of light.

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It went that way...I mean that way? Which way does this arrow point? Using physics to give bad directions.
What you Need

A glass

Water

A note card

A marker

What to Do

1. Fill your glass of water.

2. Draw a horizontal arrow on a note card.

3. Put the note card behind the glass of water and slowly move the note card back. Look through the glass from the front and observe the arrow. What appears to happen to it?

What's Going On?
No, you aren't going crazy and you haven't found yourself with Alice in Wonderland staring at arrows pointing in opposite directions. In fact, you have just demonstrated a physics concept called refraction, the bending of light.

When the arrow is moved to a particular distance behind the glass, it looks like it reversed itself. When light passes from one material to another, it can bend or refract. In the experiment that you just completed, light traveled from the air, through the glass, through the water, through the back of the glass, and then back through the air, before hitting the arrow. Anytime that light passes from one medium, or material, into another, it refracts.

Just because light bends when it travels through different materials, doesn't explain why the arrow reverses itself. To explain this, you must think about the glass of water as if it is a magnifying glass. When light goes through a magnifying glass the light bends toward the center. Where the light all comes together is called the focal point, but beyond the focal point the image appears to reverse because the light rays that were bent pass each other and the light that was on the right side is now on the left and the left on the right, which makes the arrow appear to be reversed. The diagram explains this better.

Try This!

Try using differently shaped glasses. Does the shape of glass affect the distance when the arrow reverses?

To Learn More:

Ask A Physicist: Disappearing Penny

Physics@Home: Laser Jello

PhysicsQuest 2009: Spectra

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It went that way...I mean that way? Which way does this arrow point? Using physics to give bad directions. What you Need A glass Water A note card A marker What to Do Fill your glass of water. Draw a horizontal arrow on a note card.

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Refraction and light bending (article) | Khan Academy

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As light travels through different mediums (materials or forms of matter), the rays of light refract and effect that way we see images. Refraction is the bending of light. In this example to the left, the light travels through air, glass, water, back through glass, back through air, and to the arrows. The light rays refract to a center point, or focal point, in the water. As the light goes beyond the focal point the image behind it appears reversed.

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Looking through water!