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

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Q: 53 (NDA-I/2018)

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

question_subject: 

Science

question_exam: 

NDA-I

stats: 

0,8,10,5,4,1,8

keywords: 

{'refractive index': [0, 1, 1, 5], 'material medium': [0, 0, 0, 1], 'air': [1, 0, 0, 0], 'materials': [0, 1, 1, 0], 'unity': [1, 0, 0, 5]}

The correct statement about the refractive index of a material medium with respect to air is option 4: it is always greater than one.

Option 1 is incorrect because the refractive index is always positive. It is a ratio of the speed of light in a vacuum to the speed of light in the medium, and both of these speeds are always positive values.

Option 2 is incorrect because the refractive index represents how much the speed of light is reduced when it passes through the medium compared to a vacuum. If the refractive index were zero, it would mean that the speed of light in the medium is the same as the speed of light in a vacuum, which is not the case in any material medium.

Option 3 is incorrect because the refractive index varies for different materials. It depends on the physical properties of the material, such as its density and composition.

Therefore, the correct answer is option 4: the refractive index of a material medium with respect to air is always greater than one.

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