The Total solution for NCERT class 6-12
For sound waves, the Dopplerformula for frequency shift differs slightly between the two situations: (i)source at rest; observer moving, and (ii) source moving; observer at rest. Theexact Doppler formulas for the case of light waves in vacuum are, however,strictly identical for these situations. Explain why this should be so. Wouldyou expect the formulas to be strictly identical for the two situations in caseof light travelling in a medium?
No
Sound waves can propagate onlythrough a medium. The two given situations are not scientifically identicalbecause the motion of an observer relative to a medium is different in the twosituations. Hence, the Doppler formulas for the two situations cannot be thesame.
In caseof light waves, sound can travel in a vacuum. In a vacuum, the above two casesare identical because the speed of light is independent of the motion of theobserver and the motion of the source. When light travels in a medium, theabove two cases are not identical because the speed of light depends on thewavelength of the medium.