Open-Response Homework Problem 21.1 A pane of glass, n_glaas = 1.5, is in air. L

Question

Open-Response Homework Problem 21.1 A pane of glass, n_glaas = 1.5, is in air. Light of a certain intensity strikes the pane at normal incidence; some of the light is reflected from the front surface, some of the light goes through the glass itself and is reflected from the back surface. Assume no secondary reflections. What percentage of the original light is reflected from the front surface? What percentage of the original light is reflected from the back surface? What percentage of the original light is transmitted all the way through the pane?

Explanation / Answer

Let the Intensity of the incident light = Ii
Let the Intensity of the reflected light = Ir
Let the Intensity of the transmitted light = It

R = Ir/Ii
T = It/Ii

Ir + It = Ii
R + T = 1

Where R = (1.5 - 1)^2 / (1.5 + 1)^2
R = 0.04
T = 0.96

R = Ir/Ii
Ir = 0.04 * Ii

T = It/Ii
0.96 = It/Ii
It = 0.96 * Ii

(a)
% of the original light reflected from the front surface
% of the original light reflected from the front surface = (0.04 Ii / Ii) * 100%
% of the original light reflected from the front surface = 4 %

(b)
0.96 = It /0.96 Ii
It = 0.96 * 0.96 * Ii
It = 0.9216 Ii

Ir = (0.96 - 0.9216) Ii
Ir = 0.0384 Ii

% of the original light reflected from the back surface
% of the original light reflected from the back surface  = (0.0384 Ii / Ii) * 100%
% of the original light reflected from the front surface = 3.84 %

(c)
% of the original light is transmitted all the way through the pane =
% of the original light is transmitted all the way through the pane = (0.9216 Ii / Ii) * 100%
% of the original light is transmitted all the way through the pane = 92.16 %

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