Table Of Contents: Interactions of Light
1. Reflection of Light
You can see your reflection in any shiny surface, from a metal spoon to a puddle of water. Sometimes the reflection is sharp and clear, like the reflection from a mirror. This is called regular reflection. At other times the image is fuzzy, like the reflection in moving water. This is called diffuse reflection. In a regular reflection, parallel light rays hit a smooth surface and are all reflected at the same angle. While in a diffuse reflection the light rays are reflected in different angles.
2. Refraction of Light
Light is refracted, or bent, when it passes from one substance to another. In a vacuum and in air, light travels at about 300,000 km/s. If the light travels from air to another material, such as water, the speed of light decreases. As light passes from air to water, instead of continuing in a straight line, the light ray is bent downward, or refracted. This causes an object in water to appear higher and the water to appear shallower than it really is. A material’s index of refraction, represented by n, is a measure of how much light bends when it enters that material. The higher the index of refraction the more light bends. For example, glass will bend light more than water because glass has a higher index of refraction.
3. Diffraction of Light
You can hear someone who is speaking to you from another room because sound diffracts or spreads out around openings or corners. It is harder to see the diffraction of light because light travels in a straight line. Diffraction of light can only be seen when light passes through very small openings. The molecules that make up the atmosphere can sometimes act like these tiny openings. Sunlight behind a cloud is diffracted by the air molecules in the cloud, and produces a halo around the cloud.
4. Polarized Light
Light from most sources, such as the Sun or a lamp, travels outward in all directions. Light that travels in all directions is called incoherent light. Light that travels in only one direction is called coherent or polarized light. A special filter can be used to polarize light, which only allows light traveling in one direction to pass through. This is how polarizing sunglasses reduce the amount of light you see on a sunny day. However, two polarizing filters placed at right angles to each other will not let any light to pass through. A laser produces a special kind of polarized light that has high energy.