The velocity of light emitted by a source $S$ observed by an observer $O$,who is at rest with respect to $S$,is $c$. If the observer moves towards $S$ with velocity $v$,the velocity of light as observed will be

$A$ star is moving towards the earth with a speed of $4.5 \times 10^6 \ m/s$. If the true wavelength of a certain line in the spectrum received from the star is $5890 \ \mathring A$,its apparent wavelength will be about........$\mathring A$ $[c = 3 \times 10^8 \ m/s]$

It is believed that the universe is expanding and hence the distant stars are receding from us. Light from such a star will show:

If the shift of wavelength of light emitted by a star is towards the violet end of the spectrum,then this shows that the star is

In the hydrogen spectrum,the wavelength of the ${H_\alpha}$ line is $656 \ nm$,whereas in the spectrum of a distant galaxy,the ${H_\alpha}$ line wavelength is $706 \ nm$. The estimated speed of the galaxy with respect to the Earth is:

If a star emitting yellow light is accelerated towards the Earth,then to an observer on Earth,it will appear: