Question

Light traveling through plate glass (n = 1.52) approaches the surface, i.e. the air-glass interface. What minimum incident angle must the light have in order to be totally internally reflected back into the glass? > A) 31。 B) 41。 > C) 51° D) 61。

Answer 1

Answer:

41°

Explanation:

refractive index of glass, n = 1.52

For total internal reflection, the angle of refraction in rarer medium is 90°.

r = 90°

Let the angle of refraction in denser medium, that means in glass is i.

By use of Snell's law

refractive  index of rarer medium with respect to denser medium, that means refractive index of air with respect to glass = 1 / n

And

$\frac{1}{n}=\frac{Sin i}{Sin r}$

$\frac{1}{1.52}=\frac{Sin i}{Sin 90}$

$0.658= Sin i$

i = 41°

Thus, the angle of incidence should be 41°.