Real Life Applications
6 min read

Ray Optics And Optical Instruments

- Wondering why to study this chapter? Know the real world use of it!
In binoculars, the image generated is backwards and upside down. But luckily, prism is not just a tool to split white light into 7 colours. Prisms are often used as corrective elements to fix this problem and they are situated between the objective lens and the eyepiece lens.
A pair of special prisms, known as Porro Prisms are used for each eyepiece in binoculars. These prisms are shaped and aligned such that they result in Total Internal Reflection of the incident light coming after refraction from the objective. Here, the sharpness of the image is not compromised, as 100% of the light is reflected TOTALLY and INTERNALLY!
The reflector of the headlight of any vehicle is the most common application of a curved mirror. The light source (headlight bulb) is situated in the middle of the reflector cup. This allows the light being emitted from the small bulb to be spread out in front of the vehicle. However its light pattern has intense and weak spots which may cause the blinding of oncoming traffic.
But what happens if we use a converging lens instead? We obtain an improvised lighting system called the projector lamps. The lens is placed such that the image plane of the reflector coincides with the focal point of the lens. The lens straightens out the path of the light, as it directs every beam in the same direction. Smaller the area, larger the intensity from the same lamp of a given power rating.
We can see the difference ourselves! The pattern of projector lamps is more concentrated and is more pencil beam like which prevents blinding of other drivers.
Not only on roads, optical devices help our vision under water too. The periscopes used in submarines to view the objects above the water surface use a set of prisms (marked as "b" in second figure). These prisms use total internal reflection. We could have easily used a pair of plane mirrors (as shown in first figure marked as "a") for two successive reflections. But as we know, there is 0% loss of image sharpness when we use reflecting prisms which work on the principle of Total Internal Reflection.
Spherical mirrors also find use in road safety. The rearview mirrors are concave mirrors which provide the driver a large field of vision. Concave mirrors are employed in warehouses too where there is frequent commute of loading vehicles. These help the workers there to be aware of the oncoming vehicles on sharp turns. They can be used at every turn of streets too.
Optical instruments have made our explorations of the universe so easy. Viewing the objects from microscopic level to the macroscopic has become possible due to them. Be it micro-organisms, wild-life, or extra-terrestrial bodies, microscopes, binoculars, and telescopes have literally increased our horizons of vision.
The knowledge of lenses and their power is used by opticians to find the exact lens required to correct the defect of vision.
  • Focal length of any system of lenses can be increased by introducing a diverging lens. That's why myopia is corrected using a concave lens so that image is focused at farther point, exactly on the retina.
  • Similarly, focal length of any system of lenses can be decreased by introducing a converging lens. That's why hypermetropia is corrected using a convex lens so that image is focused much closer, just where the retina is.