Notes

Interactions of Light - Carson Mulvey
1. How can matter interact with light?
- Three forms of matter-light interactions play an important role in how people see light.
- When light enters a medium, the medium lets all, some, or no light pass through.
- Matter that transmits light is transparent.
- Matter that transmits light but scatters it in all directions is translucent.
- Matter can absorb light.
- When light enters a material but does not leave it, the light is absorbed.
- Absorption is the transfer of light energy to matter.
- Opaque materials do not let any light pass through them because they reflect light, absorb light, or both. - Matter can reflect light.
- Reflection is the bouncing of light off a surface.
- When light strikes a smooth surface, the light bounces off at an angle equal to the angle at which it hit the surface, producing a clear image.
- When light strikes an uneven surface, the light is reflected in many directions.
- You see the object but do not see a reflected image of yourself.
- Nearly everything we can see, we see because light is reflected off a surface.
2. What determines the color of objects we see?
- When white light strikes an object, the color of the object depends on how the object transmits, reflects, or absorbs the colors of light.
- An object that reflects a certain color of light appears to be that color.
- A frog appears green because its skin absorbs all colors but green.
- An object that reflects every color appears white.
- An object that absorbs every color appears black.
- When light is transmitted through an object, the object can absorb some colors and allow other colors to pass through.
- The color that passes through a transparent or translucent object determines the color of that object.
- Some matter absorbs certain types of electromagnetic waves and allows other types of electromagnetic waves to pass through.
- Sometimes the color of an object depends on what light shines on it.
- If a red filter is placed between a green frog and white light, the filter will absorb all colors of light except red, orange, and yellow.
- The frog reflects no light, and you perceive the frog’s color as gray or black.
3. What happens when light waves interact with matter?
- Light travels 300 million miles per second through a vacuum.
- This is called the speed of light.
- When light waves pass through a medium, the medium can change properties of the light.
- Light goes slower when it passes through matter.
- Shorter wavelengths of light are slowed more than longer wavelengths of light.
- Light bends when it passes at an angle from one medium to another.
- The bending of a wave as it passes from one medium to another is called refraction.
- Refraction occurs because light changes speed as it enters a medium at an angle.
- When light slows in a medium, it bends inward, creating a smaller angle.
- Light waves with shorter wavelengths bend more.
- The waves that make up white light have different wavelengths.
- As white light passes through a prism, the wavelengths refract at different angles and you see a spectrum of colors.
- When light strikes matter, the light can change direction.
- This is called scattering.
- Light scattering allows us to see objects that are not in the direct path of the light source.
- Another result of scattered light is the color of the sky.
- Blue light is scattered more than other colors, so the sky appears blue.
- When the sun strikes Earth at an angle, light waves pass through more of the atmosphere.
- Only the long-wavelength red light reaches Earth.
Suitable Brainpops: Refraction/Defraction, Color, Rainbows