Question

You observe a light ray move from one piece of glass to another (a different type of glass) and the light ray bends towards the glass-glass interface (away from the normal) when it enters the 2nd piece of glass. You deduce that:
a. Glass 1 has a higher index of refraction than glass 2, and light moves faster in glass 2 than in glass 1
b. Glass 1 has a higher index of refraction than glass 2, and light moves faster in glass 1 than in glass 2
c. Glass 2 has a higher index of refraction than glass 1, and light moves faster in glass 1 than in glass 2
d. Glass 2 has a higher index of refraction than glass 1, and light moves faster in glass 2 than in glass 1

Answer 1

Answer: C

Explanation: When light rays moves from one medium to another with a change in its direction (bending towards media interface), it is called refraction.

The angle the ray in the second medium (refracted ray) makes with the medium interface (normal) explains the bending of light and is dependent on the following the refractive index (n), wave speed in the medium (v) and other properties such as wavelength, and angle of incidence.

This question is focused on the relationship between refractive index and wave speed.

Refractive index (n) is inversely proportional to wave speed (v). This implies that a ray of light moving from a dense medium (say air) to a more dense medium (say glass) has it wave speed decreased and if reversed ( from glass to air) the wave speed increases.

A change in refractive index also affects the bending of the refracted ray.

A move from a dense to a more dense medium makes the refracted ray move towards the normal thus decreasing the angle of refraction (angle the refracted ray makes with the normal)

So for our question, since light ray (refracted ray) moves towards the glass to glass interface (normal) it means that light ray had moved from a dense to a more dense medium (that is glass 2 has higher refractive index than glass one) and the wave speed will decrease since there is an increase in refractive index (that is light travels faster in glass 1 than glass 2)