JEE Main & Advanced Physics Ray Optics Common Examples of TIR

(1) Looming : An optical illusion in cold countries

(2) Mirage : An optical illusion in deserts

(3) Brilliance of diamond : Due to repeated internal reflections diamond sparkles.

(4) Optical fibre : Optical fibres consist of many long high quality composite glass/quartz fibres. Each fibre consists of a core and cladding.

(i) The refractive index of the material of the core \[({{\mu }_{1}})\]is higher than that of the cladding \[({{\mu }_{2}})\].

(ii) When the light is incident on one end of the fibre at a small angle, the light passes inside, undergoes repeated total internal reflections along the fibre and finally comes out. The angle of incidence is always larger than the critical angle of the core material with respect to its cladding.

(iii) Even if the fibre is bent, the light can easily travel through along the fibre

(iv) A bundle of optical fibres can be used as a 'light pipe' in medical and optical examination. It can also be used for optical signal transmission. Optical fibres have also been used for transmitting and receiving electrical signals which are converted to light by suitable transducers.

(5) Field of vision of fish (or swimmer) : A fish (diver) inside the water can see the whole world through a cone with.

(a) Apex angle\[=2C={{98}^{o}}\]

(b) Radius of base  \[r=h\tan C=\frac{h}{\sqrt{{{\mu }^{2}}-1}}\]; for water\[\ r=\frac{3h}{\sqrt{7}}\]     

(c) Area of base A\[=\frac{\pi {{h}^{2}}}{({{\mu }^{2}}-1)}\]; for water \[a=\frac{9\pi }{7}{{h}^{2}}\]

(6) Porro prism : A right angled isosceles prism, which is used in periscopes or binoculars. It is used to deviate light rays through \[{{90}^{o}}\]and \[{{180}^{o}}\]and also to erect the image.