Avery thin film of oil (n-1.25) sits on glass (n -1.53), what is the phase shift of the light reflected from (a) the top surface of the film? (b)the bottom surface of the film? (c) what is the thinnest film that produces a strong cancellation on the reflection at 600 nm?

240 nm

Explanation:

In the interference in thin films , light reflected from upper surface and light reflected from the lower surface of oil are made to interfere each other to form  fringes due to path difference of 2μt .

a ) An additional phase shift of 180 ° occurs on the upper surface because light is going from optically rarer medium to denser medium .

b ) There is no such change on reflection from lower surface as light is going from denser to rarer medium ( air ).

c ) For destructive interference the path difference which is equal to 2 μ t should be equal to n λ where n is any number

So for given condition

2 μ t  = n λ

For minimum thickness

2 μ t  =  λ ( n =1 )

t = λ / 2μ

= 600 x 10⁻⁹ /( 2 x 1.25 )

= 240 nm

when two balls of the different masses are dropped from equal height, they reach the ground at the same time .this is because they experience the same acceleration.

the acceleration is independent of mass.

thus when they are dropped they will always maintain the same velocity and travel the same distance (neglect air resistance of course) at the same time.

as we know our atmosphere or air have different levels. every level has other gasses, and every gas has another permeability. when the light comes from lower permeability to higher permeability, it changes its direction. so that means that when the light comes from the moon to the earth, it changes it's direction many more times. it basically means that the shape of the light part of the moon is changed on the earth.

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