12th Notes

Application of Total internal reflection

Application of total internal reflection ( T.I.R) – 

T.I.R in nature and its technological application-

Brilliance of diamond-   The brilliance of diamond is due to the total internal reflection of light. Refractive index for diamond is very large which is near about 2.42 , so that critical angle for diamond air is 24.40. The diamond is cut suitably so that light entering the diamond from any face falls at an angle greater than 24.40. Therefore , it suffers multiple T.I R. at various faces , and remains within the diamond , falling to come out . Hence the diamond sparkles.

Mirage–   Mirage is an optical illusion of water observed generally in desert in hot summer day. An inverted image of an object such as tree is observed along with the object as if the tree were on the bank of a pound of water.

Optical fibres – It is a device based on Total internal reflection by which signal may be transmitted from one location to another. It is a thin fibre of plastic specially coated glass , in which light enters at one end leaves it at other end suffering a number of total internal reflection with little loss of energy . it works even it is bent or twisted.

 The structure of The structure of optical fibre consists of a core surrounded by cladding . Core ( very high quality glass/silica/plastic) is denser medium of refractive index µ1 and cladding ( glass/plastic) is relatively rarer medium of refractive index µ2  such that µ1 > µ2 .When light incident at one end of the core gets reflected and will be incident on the interface between the core and cladding at an angle greater then the critical angle and light continues reflecting in the core. After several reflection light comes out to the other side i.e.  at the destination.   

 Application of optical fibre –

 ( I ) It is used to transmit light without loss of intensity over a long distance of several kilometers .

(ii) It is used in the in the manufacture of medical instruments, called endoscope for visual examination of stomach and intestines etc. of patients.

(iii) It used for telecommunication, i.e., in transmitting audio and video signals to long distance.

(iv) It is used to measure the blood flow to the heart in the form of photometric sensor.

(v) It is used to measure refractive indices of the liquid.

Totally reflected glass prism – Prism designed to bend light by 900, or 1800 the phenomenon of total internal reflection , such prisms are used to invert images without changing their sizes.