JEE Main & Advanced Physics Wave Optics / तरंग प्रकाशिकी Question Bank Doppler's Effect of Light

  • question_answer
    The wavelength of light observed on the earth, from a moving star is found to decrease by 0.05%. Relative to the earth the star is                                                          [MP PMT/PET 1998]

    A)            Moving away with a velocity of \[1.5\times {{10}^{5}}m/s\]

    B)            Coming closer with a velocity of \[1.5\times {{10}^{5}}m/s\]

    C)            Moving away with a velocity of \[1.5\times {{10}^{4}}m/s\]

    D)            Coming closer with a velocity of \[1.5\times {{10}^{4}}m/s\]

    Correct Answer: B

    Solution :

                       \[\frac{\Delta \lambda }{\lambda }=\frac{v}{c}\,\Rightarrow \,\frac{0.05}{100}=\frac{v}{3\times {{10}^{8}}}\] Þ v = 1.5 ´ 105 m/s (Since wavelength is decreasing, so star coming closer)


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