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# TNPSC Free Notes Physics In English – Light and its Characteristics

இந்தக் கட்டுரையில், TNPSC குரூப் 1, குரூப் 2, குரூப் 2A, குரூப் 4 மாநிலப் போட்டித் தேர்வுகளான TNUSRB, TRB, TET, TNEB போன்றவற்றுக்கான  முறைகள் இலவசக் குறிப்புகளைப் பெறுவீர்கள்.தேர்வுக்கு தயாராவோர் இங்குள்ள பாடக்குறிப்புகளை படித்து பயன்பெற வாழ்த்துகிறோம்.

### Light and its Characteristics

Light
 Light is a form of energy.
 Travels along in straight line and need not any medium for propagation.
 The speed of light c = 3 x 10 8 ms –1 .
 c = ν λ
o c – velocity of light (C)
o λ – wavelength (λ)
o v – Frequency (ν)
 Violet light – lowest wavelength.
 Red light – highest wavelength.

Laws of reflection:
 The incident ray, the reflected ray and the normal at the point of incidence, all lie in
the same plane.
 The angle of incidence (i) and the angle of reflection (r) are always equal.

Types of reflection:
Regular or specular reflection:
When a beam of light (collection of parallel rays) falls on a smooth surface, it gets reflected.
After reflection, the reflected rays will be parallel to each other

Irregular or diffused reflection:
In the case of a body having a rough or irregular surface, each region of the surface is inclined at
different angles. When light falls on such a surface, the light rays are reflected at different
angles.

Laws of refraction:
 The incident ray, the refracted ray and the normal at the point of intersection, all lie in the
same plane.
 The ratio of the sine of the angle of incidence (i) to the sine of the angle of refraction (r)
is equal to the refractive index of the medium, which is a constant.
 μ = c/v

Scattering of Light:
When sunlight enters the Earth’s atmosphere, the atoms and molecules of different gases present
in the atmosphere refract the light in all possible directions.

Types of Scattering:
Elastic scattering:
If the energy of the incident beam of light and the scattered beam of light are same, then it is
called as elastic scattering.
Inelastic scattering:
 If the energy of the incident beam of light and the scattered beam of light are
different, then it is called as inelastic scattering.
 The nature and size of the scatterer results in different types of scattering. They are
o Rayleigh scattering
o Mie scattering
o Tyndall scattering
o Raman scattering

Rayleigh scattering:
 Amount of scattering ‘S’ ∝ 1/λ 4 (S = scattering and λ is the wavelength)
 When sunlight passes through the atmosphere, the blue colour (shorter wavelength) is
scattered to a greater extent than the red colour (longer wavelength).
 This scattering causes the sky to appear in blue colour.

Mie scattering:
 Mie scattering takes place when the diameter of the scatterer is similar to or larger than
the wavelength of the incident light .
 Mie scattering is responsible for the white appearance of the clouds.
Tyndall Scattering:
 The scattering of light rays by the colloidal particles in the colloidal solution is called
Tyndall Scattering or Tyndall Effect .
 Beam of sunlight enters into a dusty room through a window, then its path becomes
visible.
Raman scattering:
 When a parallel beam of monochromatic (single coloured ) light passes through a gas or
liquid or transparent solid, a part of light rays are scattered.
 The scattered light contains some additional frequencies (or wavelengths) other than that
of incident frequency (or wavelength). This is known as Raman scattering or Raman
Effect.
Total internal reflection:
 When the angle of incidence exceeds the value of critical angle, the refracted ray is not
possible. Since r &gt; 90º the ray is totally reflected back to the same medium. This is called
as total internal reflection
 Light must travel from denser medium to rarer medium.
 Example: From water to air.

Dispersion:
 Splitting of white light into its seven constituent colours (wavelength), on passing
through a transparent medium.
 Refraction of a light ray is inversely proportional to its wavelength.

 The red coloured light, which has a large wavelength, is deviated less while the violet
coloured light, which has a short wavelength, is deviated more.
 Example – Rainbow

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