When light travels into a different medium , the speed of the light changes and the light is refracted (see The features of waves). The angle of refraction is greater than the angle of incidence . The diagram below shows the light refracting from glass into air.

Apparent depth of the pond appears to be less than the real depth only because of refraction of light, but not because of total internal reflection. On the other hand, brilliance of diamond, formation of mirage on hot summer days and working of optical fiber are based on total internal reflection.

Total internal reflection, in physics, complete reflection of a ray of light within a medium such as water or glass from the surrounding surfaces back into the medium. The phenomenon occurs if the angle of incidence is greater than a certain limiting angle, called the critical angle.

Light travels in air only. Light travels in water only. In total internal reflection, light travel from denser to rarer medium.

Applications of Total Internal Reflection of Light: The phenomenon of total internal reflection of light is used in many optical instruments like telescopes, microscopes, binoculars, spectroscopes, periscopes etc. The brilliance of a diamond is due to total internal reflection.

Total internal reflection is also used in optical fibres. An optical fibre consists of an inner core of high refractive index glass and surrounded by an outer cladding of lower refractive index. Optical fibres are useful for getting light to inaccessible places. They are used in many important practical applications.

Total internal reflection can be applied in the following: 1. Telecommunication systems 2. Automotive rain sensors and windscreen wipers 3. Optical fingerprinting devices

• Telecommunication systems.
• Automotive rain sensors and windscreen wipers.
• Optical fingerprinting devices.

Total internal reflection (TIR) is the optical phenomenon when waves travelling in one medium strike at sufficiently oblique incident angle (called the critical angle) against the boundary with another medium of lower refractive index, instead of transmitting into the second (“external”) medium at a refracted angle.

Total internal reflection is defined as: The phenomenon which occurs when the light rays travel from a more optically denser medium to a less optically denser medium. At a specific angle of incidence, the incident ray of light is refracted in such a way that it passes along the surface of the water.

θc=sin−1(n2n1) θ c = sin − 1 ⁡ ( n 2 n 1 ) for n1 > n2. Total internal reflection occurs for any incident angle greater than the critical angle θc, and it can only occur when the second medium has an index of refraction less than the first.

Refractive index is also equal to the velocity of light c of a given wavelength in empty space divided by its velocity v in a substance, or n = c/v. refractive index. Diagram of a light ray being refracted. Encyclopædia Britannica, Inc. Refractive index.

The ratio of velocities of a light ray in the air to the given medium is a refractive index. Thus, the relation between the critical angle and refractive index can be established as the Critical angle is inversely proportional to the refractive index.

The lower the refractive index, the faster the velocity of light. Medium A has the smaller refractive index. Light will travel faster through medium A at a velocity equal to the speed of light divided by the refractive index.

i Angle of deviation is directly proportional to the refractive index of the material of prism. Thus the angle of deviation increases with an increase in the refractive index of the medium. ii Angle of deviation is inversely propotional to the wavelength of the light used.

The value of sin r = 0.3333 is calculated in the second last step.

Most people are familiar with Snell’s Law because of the apparent shortening of their legs that is observed when standing in water. Snell’s Law states that the ratio of the sine of the angles of incidence and transmission is equal to the ratio of the refractive index of the materials at the interface.

/frac{sin/;i}{sin/;r}=constant=/mu Where i is the angle of incidence and r is the angle of refraction. This constant value is called the refractive index of the second medium with respect to the first. Snell’s law formula is derived from Fermat’s principle.

sinrsini​=constant, the value of constant depends upon.

Observation: If we calculate the ratio of the sine of angle of incidence and sine of angle of reflection than it will come out to be constant. Result: Ratio of sine of angle of incidence and angle of refraction is constant.

vi) When the lens is dipped to a height which is greater than the focal length of lens in air, we are able to see the image. Showing that focal length of the lens has increased water. vii) From this we conclude that the focal length of a convex lens is increased when it is kept in water.