Refraction of Light and Its Examples in everyday life with explanation
When a ray of light passes from one medium to other, it bends from its path. This phenomenon of bending is called as refraction of light. When a ray of light travels from one medium to another, the wavelength and velocity of light change but the frequency does not change.
When a ray of light enters from rarer medium to denser medium (as from water to glass), it deviate towards the normal drawn on the boundary of two medium at the incident point. Similarly in passing from denser to rarer medium, a ray deviates away from the normal. If light is incident normally on the boundary i.e. parallel to normal, it enters the second medium undeviated.
Law of refraction
- The incident ray, the refracted ray and the normal at the point of incidence all lie in the same plane.
- Snell’s law : The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant for a given medium sin(i)/sin(r) = 1µ2 ; where 1µ2 is called refractive index of second medium with respect to first medium.
- Absolute refractive index of a medium is defined as the ratio of speed of light in free space (vacuum) to that in the given medium. i.e. absolute refractive index (µ) = (Speed of light in vacuum)/(Speed of light in the medium)
- Twinkling of stars is based upon refraction.
- Due to refraction, rivers appear shallow, coin in a beaker filled with water appears raised, pencil in the beaker appear broken.
- At sunset and sunrise, due to refraction, sun appears above horizon while it is actually below horizon.
- Oval shape of sun in the morning and evening is due to refraction of light.
- The duration of day appears to be increased by nearly 4 min due to atmospheric refraction.
- Writing on a paper appears lifted when a glass slab is placed over the paper.
- The refractive index of a medium is maximum for violet colour of light and minimum for red colour of light.
- Refractive index of a medium decreases with rise in the temperature. But this variation is very small.
- An object in a denser medium when seen from a rarer medium appears to be at a smaller distance.
This is way (a) A fish in a pond when viewed from air appears to be at a smaller depth than actual depth (b) A coin at the base of a vessel filled with water appears raised.
Total Internal Reflection of Light
- When a light ray goes from denser medium to rarer medium, then as we increase the angle of incidence, angle of refraction also increases, so the angle of incidence for which the angle of refraction becomes 90° is called critical angle.
- If the angle of incidence in denser medium is greater than critical angle (C), then the ray is reflected back into the first rarer medium, this phenomenon is called total internal reflection.
- It is necessary for the total internal reflection of light to occur that light ray should go from denser medium to rarer medium.
- Angle of incidence in denser medium should be greater than critical angle.
- In desert, the phenomena of mirage occurs due to total internal reflection.
Scattering of Light
- When light passes through a medium, in which particles are suspended, whose sizes are of the order of wavelength of light, then light on striking these particles, deviated in different directions. This phenomenon is called scattering of light.
- Red colour of light is scattered least and violet colour of light is scattered most. Therefore, danger signals are of red colour.
- Blue colour of sky is due to scattering of light. The brilliant red colour of rising and setting sun is due to scattering of light.
- Clouds appear white due to scattering of light.
- Sky appears black to Astronaut from the space.
Total Internal Reflection Examples
- Sparkling of diamond is due to multiple total internal reflection taking place inside the diamond.
- Mirage and looming.
- The air bubble in glass paper weight appear silvery white due to total internal reflection.
- Increase in duration of sun’s visibility – The sun becomes visible even before sun rise and remains visible even after sunset due to total internal reflection of light.
- Shining of a smoked ball or a metal ball on which lamp soot is deposit when dipped in water.
- Optical Fiber : Optical fiber consists of thousands of strands of a very fine quality glass or quartz (of refractive index 1.7), each strand coated with a layer of material of lower refractive index (1.5). In it, light is propagated along the axis of fiber through multiple total internal reflection, even though the fiber is curved, without loss of energy.
Optical Fiber Applications
- For transmitting optical signals and the two dimensional pictures.
- For transmitting electrical signals by first converting them to light.
- For visualizing the internal sites of the body by doctors in endoscopy.
Refraction of Light Questions
- When light travel from water to air, in which direction does the light bend?
- What is the cause of refraction of light?
- Does a pool appear to be shallow when viewed normally?