Which one of the following statements about the refractive index of a

Which one of the following statements about the refractive index of a material medium with respect to air is correct ?

It can be either positive or negative

It can have zero value

It is unity for all materials

It is always greater than one

Answer is Right!

Answer is Wrong!

This question was previously asked in

UPSC NDA-1 – 2018

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The refractive index of a material medium ($n_m$) with respect to air ($n_{air}$) is defined as the ratio of the speed of light in air ($v_{air}$) to the speed of light in the medium ($v_m$). Since the speed of light in any material medium is always less than the speed of light in vacuum (and approximately less than the speed of light in air), the ratio $v_{air} / v_m$ will always be greater than 1 for any material medium (except vacuum or air itself, where the refractive index is 1).

Refractive index is a measure of how much the speed of light is reduced in a medium compared to air/vacuum. A higher refractive index indicates a slower speed of light in the medium and greater bending of light.

Refractive index values are typically positive. A refractive index of zero or negative would imply unusual optical properties, not characteristic of common materials. The refractive index of air with respect to vacuum is slightly greater than 1, but often approximated as 1. The refractive index of a medium with respect to vacuum is always greater than or equal to 1.

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