Page 143 - Science Class 07

through its side that is curved outwards. Are
Periscope Principal of Periscope
weapons and gun-fires. The periscope helps
the crew to see everything from inside the
tanks.
Besides, periscopes are used in nuclear reactors
and laboratories where scien sts use them to
observe everything keeping quite safe from
every danger.
1. What is reflec on of light?
2. What is required for the regular
reflec on of light?
3. What is incident angle?
4. Write the uses of plane mirrors.
5. Differen ate between regular and
irregular reflec on.
6. What is the use of periscope on
submarines?
SPHERICAL MIRRORS
We have learnt how plane mirrors produce
images that are erect, laterally inverted and of
the same size. But spherical mirrors are curved,
not flat like plane mirrors. So, the images
formed by them are quite different.
Take a shining steel spoon and look at your face
through its side that is curved inwards and also
Science-7
both the images same? No, they differ a lot.
Both the sides of a spoon are examples of two
types of spherical mirrors. A spherical mirror is,
indeed, a part cut off from a sphere.
The two types of mirror are as under:
Convex Mirrors
A convex mirror has its surface curved
outwards like the outer surface of a sphere.
Concave Mirrors
A concave mirror has its surface curved inwards
like the inner surface of a sphere.
Convex Mirror Concave Mirror
Let us understand the following facts about
spherical (curved) mirrors:
v The central point of a spherical mirror is its
pole and it is denoted by point P.
v The center of the sphere of which the
spherical mirror is a part is called the
center of curvature of the mirror. It is
denoted by point C.
v The straight line joining the pole (P) and
the center of curvature (C) of a spherical
mirror is the principal of the mirror.
v When parallel rays strike at a spherical
mirror, they reflect to meet at a point
called the focus of the mirror. This point is
denoted by point F.
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