Question

The chart shows the speed at which light travels through different media. In which medium would light have the longest wavelength?
water
air
glass
diamond

Answer 1

The correct answer is air.  

The refractive indexes of air, water, glass and diamond are1.0003, 1.33, 1.5 and 2.42 respectively. The refractive index of air is the lowest so it is the medium through which light will travel faster with the longest wavelength. The higher the refractive index the denser the medium and the slower is the speed with which light will travel through this medium.  

Answer 2

Answer : Option B) Air

Explanation : As the speed of light depends on the refractive index of the medium; then according to Snell's law (refer the attachment) Air is the medium that would have the longest wavelength amongst the given options.

As the refractive indexes of water is 1.33, glass is 1.5 and diamond 2.42 are much higher than air. Therefore, it will be the medium which will allow maximum light to pass through it easily and hence, will be the medium with longest wavelength.