Light Beams and Rays
When we look at an object, some
energy passes from it to our eyes and stimulates our sense of vision. The
energy which stimulates vision is called light energy, and travels at the
enormous speed of 186,000 miles per second in air. Some substances, such as
glass, allow a high proportion of light energy to pass through them, and they
are known as transparent substances. Substances which completely prevent the
light energy from passing through are known as opaque substances.
Light
travels in straight lines, which gives more evidence that light travels in
straight line is obtained when sunlight is observed streaming through an
opening into a darkened room. The dust particles are then illuminated by the
light, and a straight edge is observed at the light boundary. Shadows, too,
have sharp edge because light travels in straight line.
The ray
box, the path taken by light is known as a ray. A beam of light is the name
given to a collection of rays of light, such as those given out by a lamp, a
torch, or a searchlight. The type of beam as shown below;
Pin-hole camera
A pin-hole camera utilizes the fact that rays of light
travel in straight lines. A small pin-hole H
is made in one side of a box and an object is situated in front of H. A ray from the top point A of the
object then passes straight through H
and meet the back of the camera at B. It illustrates other rays from the object
passing straight through H, and
building up an image of the object at X
on the back of the camera. The image is clear one if each point on the object
gives rise to one point on X, but
this can only happened if the pin-hole is small. A wider hole allows rays from
a point such as A on the object to
spread over small area round B, thus
blurring the image. The pin-hole camera is sometimes preferred to the
photographic camera by surveyors, as the lens in the latter may produce distortion
when a building, for example, is photographed.
The size of the image
Book – M Nelkon M.Sc.(Lond), A.K.C
No comments:
Post a Comment