How to measure the powers of the lens
The power of
a lens is the reciprocal of its focal length expressed in meters.
Power of a lens = 1/f
The power of
a converging lens is usually taken as positive and of a diverging lens as
negative.
For example,
If the focal
length of a convex lens is 0.25m then its power is
P = 1/f = 1/0.25
= 4D (D- means dioptre which is the unit of power of the lens)
Some facts about light for learners
Light-coloured clothes are preferred in summer because light colours are poor absorbers
of heat.
Light waves
are different from sound waves. In that, light waves are electromagnetic but
sound waves are not.
Television signals
cannot be received ordinarily beyond a particular distance due to the curvature of
the earth.
The minimum
length of a plane mirror in which a person can see himself full length is should
be nearly half his height.
If you walk
towards a plane mirror at a speed of 10cm/s your image approach at a speed of
20 cm/s.
If you stand
in a room where two adjacent walls are covered with plane mirrors, the total
number of your images formed will be three.
The concave mirror
can be used to obtain the real image of an object.
For the rear
views, motorists use a convex mirror.
The dentist
uses a concave mirror.
When a
pencil is partly immersed in water in a standing position, the immersed portion
appears bent towards the water's surface.
The sun
remains visible for some time after it actually sets below the horizon. This happens due to atmospheric refraction.
If there
were no atmosphere, the length of the day would decrease.
Planets do
not twinkle. Because they are nearer to us and therefore minor variations in
their intensity are not noticeable.
When white
light passes through a glass prism, it gets dispersed into colours. Because different
colours have different speeds in the glass.
The film of the
camera is analogous to the retina in the human eye.
In old age,
people have to wear spectacles for reading and writing. Because they lose the
power accommodation.
The light
phenomenon taking place in a periscope is reflection and refraction.
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Read more:
How to measure the powers of lens and Some facts about light for learners
Reviewed by knowledge people creators
on
March 26, 2020
Rating:
Reviewed by knowledge people creators
on
March 26, 2020
Rating:
