Light travels faster in warmer air. on a sunny day, the sun can heat a road and create a layer of hot air above it. let's model this layer as a uniform one with a sharp boundary separating it from the cooler air above. use this model to explain the formation of a mirage appearing like the shiny surface of a pool of water.

Explanation:

If we assume there is a sharp boundary between the two masses of air, there will be a refraction. The refractive index of each medium will depend on the relative speeds of light.

n = c / v

If light travels faster in warmer air, it will have a lower refractive index

nh < nc

Snell's law of refraction relates angles of incidence and refracted with the indexes of refraction:

n1 * sin(θ1) = n2 * sin(θ2)

sin(θ2) = sin(θ1) * n1/n2

If blue light from the sky passing through the hot air will cross to the cold air, then

n1 = nh

n2 = nc

Then:

n1 < n2

So:

n1/n2 < 1

The refracted light will come into the cold air at angle θ2 wich will be smaller than θ1, so the light is bent upwards, creating the appearance of water in the distance, which is actually a mirror image of the sky.

the answer is a. at the equator

fgravity=10x10=100n case 1

fgravity=30x20=600n case 2

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