Question

The critical angle in air for a particular type of glass is 39.0°. what is the speed of light in this class glass? (c = 3.00 × 108 m/s

Answer 1

To get the speed of light in this class glass, used the following equation
  v= c/n ; where c is the speed of light in a vacuum and n where the index of refraction

Based on my research the index of refraction of the class glass is 1.59 

Given
  c= 3.00 x 10^8 m/s
  n= 1.59

Solution 
 we will use 3.00 for c to get the speed of light in class glass cause 10^8 m/s is fixed

v= 3.00 / 1.59
v= 1.886

So the speed of light in this class glass is 1.89 x 10^8 m/s 

Answer 2

Answer:

$v = 1.89 \times 10^8$

Explanation:

As we know that the critical angle is the maximum angle for a given medium for which light ray will show the phenomenon of refraction into air

After critical angle the light will bend into the same medium and will show total internal refraction.

So here at critical angle the angle of refraction must be 90 degree into air

So here we know

$\mu sin\theta_c = 1 sin90$

$\mu sin 39 = 1$

$\mu = \frac{1}{sin 39}$

$\mu = 1.59$

now we know by the speed of light in medium is given as

$\mu = \frac{c}{v}$

$1.59 = \frac{3 \times 10^8}{v}$

$v = \frac{3 \times 10^8}{1.59}$

$v = 1.89 \times 10^8$