refraction of light class 10 | laws of refraction class 10 | 10th class Physics | punjab, federal

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refraction of light sabaq | 10th physics wallah chapter 12 hindi | refraction of light in urdu atifahmedofficial atifahmadofficial
12.4 REFRACTION OF LIGHT
If we dip one end of a pencil or some other object into water
at an angle to the surface, the submerged part looks bent as
shown in Fig.12.7. Its image is displaced because the light
coming from the underwater portion of the object changes
direction as it leaves the water. This bending of light as it
passes from one transparent medium into another is called
refraction.
Refraction of light can be explained with the help of Fig.12.8.
A ray of light IO travelling from air falls on the surface of a
glass block.
Fig. 12.8: Refraction of light by a glass block
At the air-glass interface, the ray of light IO changes direction and
bends towards the normal and travels along the path OR inside
the glass block. The rays and OR are called the incident ray and IO
the refracted ray respectively. The angle ‘i’ made by

SUMMARY
 When light travelling in a certain medium falls on the surface of another
medium, a part of it turns back in the same medium. This is called reflection of
light. There are two laws of reflection:
i. The incident ray, the reflected ray, and the normal all lie in the same plane.
ii. The angle of incidence is equal to the angle of reflection (i.e., i = r).
 Like plane surfaces, spherical surfaces also reflect light satisfying the two
laws of reflection.
 In mirrors, image formation takes place through reflection of light while in
lenses image is formed through refraction of light.
 The equation relating the distance of the object p from the mirror/lens,
distance of the image q and the focal length f of the mirror/lens is called
mirror/lens formula, given by
 Magnification of a spherical mirror or thin lens is defined as “the ratio of the
image height to the object height.” i.e.,
 Power of a lens is defined as “the reciprocal of its focal length in metres”. Thus Power
of a lens = P = 1 / focal length in metres. The SI unit of power of a lens is “Dioptre”,
-1 denoted by a symbol D. If is expressed in metres so that 1 D = 1 m . Thus, 1 Dioptre f
is the power of a lens whose focal length is 1 metre.
 The refractive index ‘n’ of a material is the ratio of the speed of light ‘c’ in air to the
speed of light ‘v’ in the material, thus
 The bending of light from its straight path as it passes from one medium into another
is called refraction.
 Refraction of light takes place under two laws called laws of refraction. These are
stated as:
i. The incident ray, the refracted ray, and the normal at the point of incidence

The angle of incidence for which the angle of refraction becomes 90 is called critical
angle. When the angle of incidence becomes larger than the critical angle, no
refraction occurs. The entire light is reflected back into the denser medium. This is
known as total internal reflection of light.
 A simple microscope, also known as a magnifying glass, is a convex lens which is
used to produce magnified images of small objects.
 A compound microscope is used to investigate structure of small objects and has
two converging lens, the objective and the eyepiece.
 Telescope is an optical instrument which is used to observe distant objects using
lenses or mirrors. A telescope that uses two converging lenses is called refracting
telescope. A telescope in which the objective lens is replaced by a concave mirror is
called reflecting power telescope.
 The magnifying power is defined as “the ratio of the angle subtended by the image as
seen through the optical device to that subtended by the object at the unaided eye”.
 The resolving power of an instrument is its ability to distinguish between two closely
placed objects.
 The ability of the eye to change the focal length of its lens so as to form a clear image
of an object on its retina is called its power of accommodation.
 The disability of the eye to form distinct images of distant objects on its retina is
known as nearsightedness. The nearsighted eye can be corrected with glass or
contact lenses that use diverging lenses Light rays from the distant objects will .
diverge by this lens before entering the eye.
 The disability of the eye to form distinct images of nearby objects on its retina is
known as farsightedness. This defects can be corrected with the aid of a suitable
converging lens. The lens refracts the light rays more towards the principal axis
before they enter the eye.


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