Light and Rays

Reflection and Refraction

Key Question:How do we describe

the reflection and refraction of light?

Reflection and Refraction The overall study of how light behaves is

called optics. The branch of optics that focuses on the

creation of images is called geometric optics, because it is based on relationships between angles and lines that describe light rays.

Reflection and Refraction

A lens is an optical device that is used to bend light in a specific way.

A converging lens bends light so that the light rays come together to a point.

A diverging lens bends light so it spreads light apart instead of coming together.

Reflection and Refraction Mirrors reflect light and allow us to see ourselves. A prism is another optical device that can cause

light to change directions. A prism is a solid piece of glass with flat polished

surfaces.

Reflection

Images appear in mirrors because of how light is reflected by mirrors.

The incident ray follows the light falling onto the mirror.

The reflected ray follows the light bouncing off the mirror.

Reflection In specular reflection each incident ray

bounces off in a single direction. A surface that is not shiny creates diffuse

reflection. In diffuse reflection, a single ray of light

scatters into many directions.

Law of Reflection

The angle of incidence equals the angle of reflection.

The incident ray strikes the mirror.

The reflected ray bounces off.

Law of reflection

A light ray is incident on a plane mirror with a 30 degree angle of incidence.

Sketch the incident and reflected rays and determine the angle of reflection.

30o 30o

Refraction

Light rays may bend as they cross a boundary from one material to another, like from air to water.

This bending of light rays is known as refraction.

The light rays from the straw are refracted (or bent) when they cross from water back into air before reaching your eyes.

RefractionWhen a ray of light crosses from one material to another,

the amount it bends depends on the difference in index of refraction between the two materials.

Index of refractionThe ability of a material to bend rays of light is

described by the index of refraction (n).

Dispersion and prisms

When white light passes through a glass prism, blue is bent more than red.

Colors between blue and red are bent proportional to their position in the spectrum.

Dispersion and prisms

The variation in refractive index with color is called dispersion.

A rainbow is an example of dispersion in nature.

Tiny rain droplets act as prisms separating the colors in the white light rays from the sun.