The speed of light in a certain medium is 1.5 x 10^8 m/s. Taking the speed of light in vacuum as 3 x 10^8 m/s, what is the absolute refractive index of the medium?

1. Absolute refractive index n = (velocity in vacuum) / (velocity in medium). 2. Substitute: $n = \dfrac{3 \times 10^8}{1.5 \times 10^8}$. 3. Compute: $n = 2$. 4. The value 0.5 is the inverted ratio (medium over vacuum), which is rejected because n of a real medium is greater than 1. _Source: Balbharati (Maharashtra Board) Class 10 Science & Technology, Ch 6 "Refraction of Light", p.88_