Question

Atmospheric refraction causes various cool phenomena that we see around us on daily basis. The refractive index depends on the density of the material and thus the refractive index of atmosphere decreases with height. This causes the light rays to bends toward the normal as it reaches the surface of the earth.
Based on the passage answer the given two questions:


(i) Which effect is seen during the sunrise and the sunset due to the bending of sunlight as it enters the earth’s atmosphere?
(A). Early sunrise
(B). Delayed sunrise
(C). Early sunset
(D). Delayed sunset

(ii) In an Arctic region object appears to float in the air and the phenomena is called looming. In this case the refractive index of the region closer to surface has ________ refractive index than that far above the surface.
(A). greater
(B). less
(C). the same
(D). infinite

Answer 1

(A)

• During sunrise or sunset, the sun is just below the horizon.
• At these times, the sunlight has to travel the maximum distance along the Earth’s atmosphere.
• The light ray coming from the top most point (the one which is nearer to horizon) before it actually reaches the horizon bends toward the earth as it enters the earth’s atmosphere making it visible even if it is actually below the horizon.
• Usually, there is an approximate time difference of 2 minutes due to atmospheric refraction.
• Similarly, during sunset even though the sun is below the horizon the rays coming from the point near to horizon bends toward the earth and make it visible.
• So, the sun is visible to us from about 2 min even after it goes below the horizon.
• This is known as early sunrise and delayed sunset.

(B)​

• In cold regions, the air just above the ice or surface of the earth is obviously colder than that far above it.
• So, for a certain thickness (height) of the air volume, the density of it decreases with height.
• The refractive index of air in this case decreases with height
• Thus, a ray from an object going above will bend away from the normal.
• At a certain point, as the ray is going above from a denser medium to rarer medium, it undergoes total internal reflection and comes back to the surface of earth.
• If this light ray is seen, we will imagine that the object is floating somewhere in the air.
• This is called looming.