Question

Explain doppler effect in light. Distinguish between redshift and blueshift.

Answer 1

Hint: Study about the wavelength and frequency of light and imagine if the wavelength of light can be changed in some way. Consider observers or sources in motion. Consider situations like when they are going away from each other or coming towards each other.

Complete step by step answer:
Doppler effect can be observed in all the electromagnetic spectrum. It is just like the doppler shift in sound waves when the waves are expanded or squeezed in but here the speed is in terms of the speed of light. So, it is a relativistic effect.
Doppler effect of light can be defined as the change in wavelength of light when both the observer or the source or both move away from each other or come towards each other.
When the source moves away from the observer the wavelength of the observed light will be longer than the wavelength of the emitted light by the source. This is called the redshift of light. The observed wavelength of light can be expressed by the mathematical expression as,
${{\lambda }_{\text{observed}}}={{\lambda }_{\text{source}}}\sqrt{\dfrac{1+\dfrac{v}{c}}{1-\dfrac{v}{c}}}$
Again, when the source moves towards the observer the wavelength of the observed light will be shorter than the emitted light, this is called the blue shift. The observed wavelength of light is given by,
${{\lambda }_{\text{observed}}}={{\lambda }_{\text{source}}}\sqrt{\dfrac{1-\dfrac{v}{c}}{1+\dfrac{v}{c}}}$

Note: The doppler effect of light is also called the relativistic doppler effect of light. This phenomenon can be observed with the relative motion of the observer or source or both. Even if the observer is moving away or moving towards the source, the observer will see the effect of doppler shift.