The refractive index is maximum for violet colour of light and minimum for red colour of light . i . e ., μ v > μ R therefore critical angle is maximum for red colour of light and minimum for violet colour of light , i . e ., C v < C R
Total internal reflection occurs if angle of incidence in denser medium exceeds critical angle .
Mirage is an optical illusion observed in deserts and roads on a hot day when the air near the ground is holler and hence rarer than the air above .
Optical Fibres
Optical fibres are also based on the phenomenon of total internal reflection . Optical fibres consist of several thousands of very long fine quality fibres of glass or quartz . The diameter of each fibre is of the order of 10-4 cm with refractive index of material being of the order of 1.5 . Optical fibres are used in transmission and reception of electrical signals by converting them first into light signals . For Refraction at a Convex or Concave Spherical Surface
where , μ = refractive index , u = distance of object , v = distance of image and R = radius of curvature of the spherical surface
Lens
A lens is a uniform transparent medium bounded between two spherical or one spherical and one plane surface .
Convex Lens
A lens which is thinner at edges and thicker at middle is called a convex or converging lens .
Concave Lens
A lens which is thicker at edges and thinner at middle , is called a concave or diverging lens .