Question

A completely transparent material will be invisible in vacuum when the refractive index $\mu$ of material is:

• A. unity
• B. more than unity
• C. less than unity
• D. equal to 1.33

Answer 1

The correct option is A unity

An object is seen mostly due to reflection of light rays from the object. Now, if the object is completely transparent, it will not reflect light. Then it can be seen only if light rays suffer refraction while passing through the object.
After refraction, light changes its speed and hence wavelength. So, refracted light, having a different wavelength, will create a sensation of the object in our eyes.
And the transparent material will not be seen, if light rays do not suffer refraction through it. That is possible only when the refractive index of the material / object is exactly equal to the refractive index of vacuum, i.e., unity.