The rain bow apprears normally for us the observers on the earth appearing in the sky, opposite to sun . But rain bow can happen anywhere a spray of water sprinkling situation exits and a bright light is passing through it (preferably from behind the observer for good vissibility).The happenig of rain bow is on account of the principle of dispersion of light due to refraction and the principle of total reflection of the light through a collection of water droplets ,each acting as a tiny prism. The rain bow is thus an observer's eye specific, and it is not created or formed on anything like a screan, cloud or hill. In physics the phenomina could resemble a virtual image and not real image like.
The shape of rainbow is an arc or full circle depending on the obervers place.This is so because, the sensation of the rain bow to the oberving eye is particularly due to only those droplets of rain acting like of the small prisms on the vision cone of the observers eye. The refraction and total reflection happens at all angle of incidence but it is of maximum intensity when the incident sun ray on the rain droplet and refracted and totally reflected ray recieved by the eye, make an angle of 40 to 42 degree(approx). Therefore the rain droplets that are at 42 degree at our vision cone (the vertex of the vision cone subtending 40 to 42 degree at the observers eye) are resposible for the sensation of circular arc . The upper part of the circular arc , therefore, appears to have emanated from the sky, whereas the other part appears to have hidden below the horizon.
A person travelling in an aeroplane could sense a full circular shape of rainbow.A person on the top of a hill can also sense circular rainbow when the sun is behind and the rays are incident on water dropplet below the horizon due to rain , water fall or mist.
Hope this helps.
No comments:
Post a Comment