Question 4: Some stars are observed to be reddish and some are blue. Which stars have the higher temperature? Explain.

Variation in the colors of stars is a direct measure of the surface energy of the respective stars. As a particular color corresponds to a particular wavelength, therefore, the energy of the stars can be determined by the wavelengths of the color they emit.

We know that the blue light has a wavelength of 4860*10-10 m and the wavelength of red light is 6563*10-10 m.

Now Wienâ€™s displacement law says the wavelength of the emitted radiation is inversely proportional to the absolute temperature of radiation on the surface. Mathematically,

The value of the constant is 2.9*10-3 m K.

Now put the value of the wavelength of blue light star,

This is the temperature of the blue star.

Now put the value of the wavelength of the red light star,

This is the temperature of the red star.

Both equations show the surface temperature of the blue star is higher than the red star.