Physics » Notes » Reflection
Reflection :
When a ray of light falls on a surface and returned into the same media, then this phenomenon, is called reflection of light.
Laws of Reflection :
The reflection at a plane surface always takes place in accordance with the following two laws :
(i) The incident ray, the reflected ray and normal to surface at the point of incidence all lie in the same plane.
(ii) The angle of incidence, i is equal to the angle of reflection r, i. e., ∠i = ∠r.
Figure-1 : Reflection
Where,
i = Angle of incidence
r = Angle of reflection
#Note :
1. After reflection velocity, wavelength and frequency of light remains same but intensity decreases.
2. If light ray incident normally on a surface, after reflection it retraces the path.
Total Internal Reflection :
When Angle of incidence exceeds the critical angle than light ray comes back in to the same medium after reflection from interface. This phenomenon is called Total internal reflection.
When a ray of light goes from denser to rarer medium it bends away from the normal and as the angle of incidence in denser medium increases, the angle of refraction in rarer medium also increases and at a certain angle, angle of refraction becomes 900, this angle of incidence is called critical angle.
Figure-2 : Total internal reflection
Where,
i = Angle of incidence
r = Angle of reflection
C = critical angle
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- Physics » Notes » Refraction Refraction : The bending of the ray of light passing from one medium to the other medium is called refraction. Laws of Refraction : The refraction at a plane surface always takes place in accordance with the following two laws : (i) The incident ray, the reflected ray and normal to surface separating two medium all lie in the same plane. Figure-1 : Refraction (ii) The ratio of sine of the angle of incidence to the sine of the angle angle of refraction (r) is a constant called refractive index. For two media, Snell's law can be written as : Refractive Index : The ratio between the speed c of light in vacuum to the speed v in a given material is called the index of refraction μ of that material : Refractive index of a medium is that characteristic which decides speed of light in it. It is a scalar, unit less and dimensionless quantity. Dependence of Refractive index : (i) Nature of the media of incidence and refraction. (ii) Colour of light or wavelength of light. (iii) Temperature of the media : Refractive index decreases with the increase in temperature.