REFRACTION IN LIGHT:

The refraction of light is the bending of light rays as it passes from

one medium to another, thereby changing the path of the rays.

Sound and water waves also experience refraction. Refraction

makes it possible for us to have optical instruments such as
magnifying glasses, lenses and prisms. Refraction of light also helps
us to focus light on our retina. The speed of light is maximum in
vacuum.

Refraction from rarer to denser medium

Refraction occurs due to a change in the speed of the light ray or
wave. When light travels from a less denser medium (say air) to a
denser medium (say glass), the speed of light is reduced as more
light particles collide with the particles of the denser medium, thus
reducing the speed of light and bending it toward the normal to the
boundary between the two media.

Refraction from denser to rarer medium

When light rays pass through rarer to a denser medium, the light
rays bend towards the normal. Due to this the angle of refraction is
smaller than the angle of incidence. e.g. In the case when light rays
pass from air to water or from air to glass, it bends towards normal.
It is because of the reason that the speed of light rays reduces while
passing from air to glass or water. When light travels from a denser
medium to a less denser medium, the speed of light is increased as
the light particles collide with less particles of the lighter medium,
thus increasing the speed of light and bending it away from the
normal to the boundary between the two media.
Some examples:
Pool of water appears to be less deep than it actually is.
Light from the bottom of the pool when it enters the atmosphere,
deviates and bends towards the normal, giving the impression that
the bottom of the pool is elevated. The pool therefore appears to be
less deeper.

For the same explanation, A pencil dipped in a glass of water

appears to be bent.

Twinkling of stars in a clear sky.

The starlight undergoes several refractions while reaching the
Earth. This atmospheric refraction occurs in a medium of gradually
changing refractive index. Light from stars travels through different
layers of atmosphere which are denser at some points and less
denser at other . There is refraction of light from the star at each of
such point giving the appearance that the star is twinkling.

Why is a rainbow a refraction?

Rainbows are formed when light from the sun is scattered by water
droplets (e.g. raindrops or fog) through a process called refraction.
Refraction occurs when the light from the sun changes direction
when passing through a medium denser than air, such as a
raindrop. This bending by refraction makes it possible for us to
have lenses, magnifying glasses, prisms and rainbows.

What is refraction of the eye?

Refraction is the bending of light rays as they pass through one
object to another. The cornea and lens bend (refract) light rays to
focus them on the retina. When the shape of the eye changes, it
also changes the way the light rays bend and focus — and that can
cause blurry vision.15

What is the law of refraction? Snell’s law.

Laws of refraction state that:

(i) The incident ray refracted ray, and the normal to the
interface of two media at the point of incidence all lie on the
same plane.
(ii) The ratio of the sine of the angle of incidence to the sine
of the angle of refraction is constant. This is also known as
Snell's law of refraction.
sin i / sin r = Constant (n)

where i is the angle of incidence, r is the angle of refraction,

the constant value depends on the refractive indexes of the
two mediums.

Snell's law gives the degree of refraction and relation between the
angle of incidence, the angle of refraction and refractive indices of a
given pair of media. We know that light experiences the refraction
or bending when it travels from one medium to another medium.
Snell's law predicts the degree of the bend.
Snell’s Law provides a quantitative description of the amount of
bending of a wave, that depends on the refractive index of the
two mediums.

Reflection of Light:
When a ray of light strikes a smooth polished surface, it bounces back.
This is called reflection of light. The incident light ray that lands on the
surface is reflected off the surface. The ray that bounces back is called
the reflected ray.

Difference between Reflection and Refraction of Light:

Reflection is the act of light reflecting back when it hits a medium on a
plane. Refraction is the process by which light shifts its path as it travels
through a material, causing the light to bend. Thus, this is the key
difference between reflection and refraction.

DIFFERENCE BETWEEN REFLECTION AND REFRACTION

Reflection Refraction

This phenomenon usually This phenomenon usually

occurs in mirrors. occurs in lenses.

Reflection is bouncing back Refraction is shifting of speed

of light when it strikes the and direction of light when it
medium on a plane. passes through a medium
leading to the bending of light.

The light entering the medium The light entering the

medium
returns to the same medium. travels from one medium to
another.

Considering the light waves, During refraction, the light

waves
they bounce from the plane pass through the surface while
and change direction. simultaneously changing both
direction and medium.

The angle of incidence of the The angle of incidence is not

light is equal to the angle of equal to the angle of refraction
reflection.

Definitions of important terms used in studying Refraction:

Normal The point of the surface at which an optical

phenomenon occurs is called the normal. In simple
words, it is termed the point of incidence. It is shown
by a dotted line drawn perpendicular to the surface
of the refracting material, in a ray diagram.

Incident Ray The light rays that strike the refracting surface, at
the separation of two media are called the Incident
Ray.

Refracted Ray The light rays that bend after passing into
another
medium are called the Refracted Ray.
Angle of Incidence This is the angle between the
incident ray
and the normal. It is represented by ∠i and it is also
called an Incident angle.

Angle of Refraction This is the angle between refracted ray

and the normal. It is represented by ∠r and it is also
called a Refracted angle.

What is the Refractive Index?

The Refractive index also called the index of refraction enables us
to know how fast light travels through the material medium.
Refractive Index is a dimensionless quantity. For a given material
or medium, the refractive index is considered the ratio between
the speed of light in a vacuum (c) to the speed of light in the
medium (v) on which it goes. The Refractive index for a medium is
represented by small n, and it is given by the following formula:

n=c/v
where
 c is the speed of the light in a vacuum, and
 v is the speed of light in the medium.

The given velocities of light in different media can give the

refractive index by the following also where the first medium is not
vacuum:
n21 = v1 / v2
where n21 is the refractive index of 2 with respect to 1.

Based on the given refractive index of the material or medium, the

light ray either changes its direction or bends at the junction which
separates the two given media. If the light ray travels from a
certain medium to another of a slightly higher refractive index, it
bends towards the normal in that case when traveling from rarer to
a denser medium, or else it bends away from the normal when
traveling from denser to rarer medium.