Physics Chapter 26: The Refraction of Light Lenses and Optical Instruments

Interface

The boundary between two materials.

Refraction

The change in the direction of travel of light as it passes from one material to another.

Index of refraction

The ratio of speed of light in a vacuum to the speed of light in a particular material.

Apparent depth

The depth of a submerged object as seen by someone not under the water. The apparent depth is smaller than the actual depth of the object due to the refraction of light as it travels from the water into the air.

Critical angle

The angle of incidence at which the angle of refraction is 90 degrees.

Total internal reflection

The phenomenon in which a light ray incident on an interface is totally reflected and no refraction occurs at an interface.

Brewster angle

The angle of incidence of a light ray at which the reflected ray is completely polarized. At this angle the reflected and refracted rays are 90 degrees to each other.

Dispersion

The spreading of light into its color components.

Focal point

The point where a lens focuses light rays that are near the principle axis and parallel to it.

Focal length

The distance between a lens and its focal point.

Converging lens

A lens which causes incident parallel rays to converge at the focal point.

Diverging lens

A lens which causes incident parallel rays to diverge after passing through the lens, the rays then appearing to come from the focal point.

Refractive power

A figure of merit of a lens measured in diopters and given by 1/f, where f is the focal length of the lens in meters.

Angular size

The angle an object subtends at the eye of the viewer.

Angular magnification

The ratio of the final angular size produced by an optical instrument to the reference angular size of the object.

Spherical aberration

An effect in which rays from the outer edge of a spherical lens are not focused at the same point as rays that pass through the center of the lens, thus causing images to be blurred.

Chromatic aberration

An undesirable lens effect arising when a lens focuses different colors at different points.