Question

Explain Wien’s law and why our eyes are sensitive only to visible rays?

Answer 1

Wien’s law and Vision: The Sun is approximately taken as a black body. Since any object above 0 K will emit radiation, Sun also emits radiation. Its surface temperature is about 5700 K. By substituting this value in the equation of Wien’s law.

`λ_"m" = "b"/"T" = (2.898 xx 10^-8)/5700 ≈ 508  "nm"`

It is the wavelength at which the maximum intensity is 508 nm. Since the Sun’s temperature is around 5700 K, the spectrum of radiations emitted by the Sun lies between 400 nm to 700 nm which is the visible part, of the spectrum. It is shown in Figure.

                       Wavelength (nm)

             Wien’s law and Human’s vision

The humans evolved under the Sun by receiving its radiation. The human eye is sensitive only in the visible not in infrared or X-ray ranges in the spectrum.
Suppose if humans had evolved on a planet near the star Sirius (9940 K), then they would have had the ability to see the Ultraviolet rays!