Man's physical universe

xanabras

UNIT VI

SECTION 5

LIGHT MAY BE REFLECTED AND REFRACTED

Introduction.

The reflection and refraction of light have many important applications

today. Many of our most important scientific instruments,

such as the telescope and the microscope, depend upon these properties

of light.

A Few Terms Used in Connection with the Propagation of Light Are

Defined.

Light travels through space without loss of energy, but when it

travels through matter such as water or glass, a small amount of energy

is absorbed ; such materials are said to be transparent. Some materials,

like frosted glass, which scatter most of the incident light, are said to be

translucent. Other materials, like wood or stone, which transmit no

light, are said to be opaque.

When light is thrown back upon striking a surface, it is said to be

reflected. The ray striking the surface is called the incident ray, and

the ray leaving the surface is called the reflected ray. That portion of

light which is lost when a beam of light passes through a transparent

medium or when it is reflected from a medium is said to be absorbed.

Light which is absorbed is changed into some other form of energy

such as chemical energy, electrical energy, or heat energy. When light

changes its direction as it passes from one medium to another, it is

said to be refracted. When light strikes the edge of a body or passes

through a small aperture, the light does not cast a sharp shadow

because a portion of the light deviates from its course, i.e., it spreads

out. This spreading-out of light is called diffraction. The diffusion, or

scattering, of light is different from diffraction in that it is the result of

multiple reflections from rough surfaces.

Light Travels in a Straight Line.

Light travels in a straight line in a vacuum or in any homogeneous

transparent medium. The path of a projector light in a smoke-filled

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