Question

If the colour of the star is changing from red to blue it means
A. The star is going away from the earth
B. The star is coming near the earth
C. The star is stationary
D. None of these

Answer 1

Hint: The colour change phenomenon is due to the fact that wavelength of the light emitted by star changes and the frequency of the light emitted by the star also changes. Also, Different colours of stars indicate that they have different temperatures. The hottest stars tend to appear blue while the coolest stars tend to appear red in colour.

Complete answer:
As we know that the colour of the star is changing from red to blue it means that the wavelength of the light emitted by the star is decreasing, because red light has longer wavelength and blue light has shorter wavelength. The wavelength of red light has a range of nearly 620 to 750 nm, and the blue light has a range of nearly 450 to 495 nm. This means that the frequency of the light emitted by the star is increasing because the wavelength is inversely proportional to the frequency. Which implies that the star is coming near to the earth.

Therefore option (B) is the correct answer.

Additional information:
As we know that stars emit colours of different wavelengths of light with respect to its frequency. But the wavelength of the light emitted by the stars depends on the surface temperature of the star, the hotter the surface temperature of the star, the more blue colour and cooler the surface temperature of the star the more red it is.

Note:
We can note here that the colour of the star is linked to its surface temperature. The hotter the star the shorter will be the wavelength of light emitted by the star. Also one must remember the wavelength of various colours to solve such types of questions.