Interactions of Light Waves

Reflection• Reflection occurs

when light or any other wave bounces off an object.

• Law of Reflection

The angle of incidence is equal to the Angle of Reflection

Absorption

• Absorbtion- The transfer of energy carried by light waves to particles of matter.– You see this when you

shine a flashlight in the air. As the light travels from the flashlight, air particles absorb some energy and the light becomes more dim.

Scattering

• Scattering- The release of light energy by particles of matter that have absorbed energy.– As light from the

flashlight is scattered out of the beam by air particles, you are able to see objects outside of the beam.

Blue Sky

• Shorter wavelengths scatter more than light with longer wavelengths.

• As sunlight travels through the atmosphere, air molecules scatter light waves with shorter wavelengths. Blue is the most affected wavelength because it the shortest.

Refraction

• The bending of a wave as it passes at an angle from one medium to another.

• This occurs because the speed of light varies depending upon the material through which it travels.

Diffraction

• The bending of waves around barriers or through openings.

• The amount a wave diffracts depends on its wavelength and the size of the barrier or opening.

• The greatest amount of diffractions occurs when the barrier or opening is the same size or smaller then the wavelength. Since light waves are so small, in order for them to diffract much, the opening must be very narrow.

Diffraction

No Diffraction

What’s the Property of Light?

• The following slides pose discrepant events. The solution involves one of the light interactions previously discussed.

• Using the handout, draw a neat and labeled diagram of the set up.

• Next describe your observations.

• Last, explain how it works using the different forms of light interaction.

The Ghostly Container

• Set a mirror on the measuring tape at a right angle and place the container to the left and a few cm in front of the mirror.

• Go to the right side of the container and look just barely over the surface at the image of the container.

• Place a second container behind the mirror to show where the image of the container appears to be.

• Measure the angles and distances of the first candle with the angle and distances of the second container.

The Law of Reflection (angle of incidence is equal to the angle of reflection).If the lines are drawn carefully, the distances and angles should be identical.

The Ghostly Container and the Law of Reflection

Pouring Light

• Covering the hole on the can, fill the can with water.

• Shine the flashlight into the top of the can.

• Observe what happens as the water pours out.

• What happens when put your hand lower, under the water?

• Internal Reflection- The water bends the light at an angle. In order for the light to escape out of the water, it has to have an angle greater than 49˚. Since the angle is less then 49˚, it is reflected back into the water stream.

Disappearing Penny

• Place a penny under a beaker and look though the side of the glass. Pour the liquid into the container. What do you see?

Refraction- When water is added to the container, the light from the coin is bent upward so much that it goes out of the top of the glass. Since light could not get out through the side, when viewed from the side, it could not be seen.

Scattering Milk• Fill a clear bottle with water• Turn the lights off and shine a flashlight through the water.

Look at the water from all sides of the bottle. Describe what you see.

• Add a few drops of milk to the water and shake the bottle to mix it.

• Describe any color changes. Add more milk until you do.• When viewing the bottle from the side, you should see a

bluish color from blue light being scattered. If looking straight through the water toward the flashlight, the light appears reddish.

• How does this relate to air particles in the atmosphere?• The milk particles scatter the light traveling through the water

just like air particles scatter sunlight as it travels through the air.

Reverse the Arrows

• Place a row of many short arrows on a strip of paper. Then slowly pass the paper behind a full beaker of water. Then move the paper back about 10 to 20 cm and make several passes. What do you see?

Refraction- The beaker becomes a convex lens (a lens that is thicker in the middle).

Lenses

Light that shines through a convex lens comes to a focus, or converges. The beaker of water acts as a very thick convex lens. As you get back beyond the focal point, the

image reverses.