Question

When light travels from a rarer to a denser medium, the speed of light in the medium:

• A. Increases
• B. Decreases
• C. Remains the same
• D. First increases and then decreases

Answer 1

The correct option is B Decreases

Speed of light is lower in optically denser medium by definition of refractive index. Refractive index of a medium 1 wrt another medium 2 is defined as:

${\mu }_{21}=\frac{v_1}{v_2}$

where:

$v_1;$ speed of light in medium 1

$v_2:$ speed of light in medium 2

When, light travels from rarer to denser medium,

${\mu }_{21}>1$

$v_2<v_1$

Hence, speed reduces