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I understand that 4% of the light is reflected back from the glass surface in a thick glass mirror. But why 4%? Why not 5% or 10%? Will this percentage change if the glass has a lower refractive index?
Neglecting surface irregularities and assuming the light strikes at a normal angle (perpendicular to the surface), the amount of light reflected by transparent surface is given by the equation R=(1-n/1+n)2, where R is the amount of light reflected and n is the refractive index. Glass with a refractive index of 1.5 gives us: R=(1-1.5/1+1.5)2, which comes out to be R=0.04, which is 4%.I understand that 4% of the light is reflected back from the glass surface in a thick glass mirror. But why 4%? Why not 5% or 10%? Will this percentage change if the glass has a lower refractive index?
Thank you!Neglecting surface irregularities and assuming the light strikes at a normal angle (perpendicular to the surface), the amount of light reflected by transparent surface is given by the equation R=(1-n/1+n)2, where R is the amount of light reflected and n is the refractive index. Glass with a refractive index of 1.5 gives us: R=(1-1.5/1+1.5)2, which comes out to be R=0.04, which is 4%.
With a refractive index of 2: R=(1-2/1+2)2, or R=0.111..., which is about 11.1%.
With a refractive index of 1.1: R=1-1.1/1+1.1)2, or R=0.002268, about 0.2%.
Finding the amount of light reflected when the light is striking at an angle other than normal is much more complicated.
Indeed. To my knowledge, pretty much all telescope mirrors are front-surface reflective.This is why accurate mirrors as are needed for astronomy and laser work are front-surface reflective.