Class 10, Science, Chapter-9, Lecture-4, Refraction (Notes)
REFRACTION OF LIGHT:
The bending of a ray of light due to change in its speed as it passes from one medium to another is called refraction of light.
LAWS OF REFRACTION OF LIGHT:
- The incident ray, the refracted ray and the normal to the interface of two transparent media at the point of incidence, all lie in the same plane.
- SNELL’S LAW OF REFRACTION
The ratio of sine of angle of incidence to the sine of angle of refraction is constant for the light of a given colour and for the given pair of media.
i.e. ${{\sin \,\angle i} \over {\sin \,\angle r}}\,\, = \,\,n$ where is a constant called refractive index
REFRACTIVE INDEX:
The ratio of the speed of light in first medium to that in the second medium is termed as refractive index of second medium with respect to the first medium.
Mathematically ${n_{21}}\,\, = \,\,{{{v_1}} \over {{v_2}}}\,\,\,$
where
${v_1}$ is the speed of light in the first medium ,
${v_2}$ is the speed of light in the second medium.
ABSOLUTE REFRACTIVE INDEX:
The ratio of the speed of light in vacuum to that in the medium is termed as the absolute refractive index of the medium.
Mathematically $n\,\, = \,\,{c \over v}\,\,\,$
where
$v$ is the speed of light in the medium
$c$ is the speed of light in vacuum.
FACTORS ON WHICH REFRACTIVE INDEX DEPEND:
- Material of the medium.
- Wavelength of light.
Refractive Index is independent of the angle of incidence.
OPTICALLY DENSER MEDIUM:
A medium in which the speed of light is comparatively less is called optically denser medium.
- Denser medium has higher refractive index.
OPTICALLY RARER MEDIUM:
A medium in which the speed of light is comparatively more is called optically rarer medium.
- Rarer medium has lower refractive index.
LATERAL DISPLACEMENT:
The perpendicular distance of separation between the emergent ray and the original path of the incident ray is called lateral displacement.
Factors Affecting Lateral Displacement:
- Thickness of the medium.
- Angle of incidence.
- Refractive index of the medium.