JEE Main & Advanced Physics Wave Optics / तरंग प्रकाशिकी Question Bank Critical Thinking

  • question_answer
    In hydrogen spectrum the wavelength of \[{{H}_{\alpha }}\] line is 656 nm whereas in the spectrum of a distant galaxy, \[{{H}_{\alpha }}\] line wavelength is 706 nm. Estimated speed of the galaxy with respect to earth is       [IIT-JEE 1999; UPSEAT 2003]

    A)            \[2\times {{10}^{8}}m/s\]      

    B)            \[2\times {{10}^{7}}m/s\]

    C)            \[2\times {{10}^{6}}m/s\]      

    D)            \[2\times {{10}^{5}}m/s\]

    Correct Answer: B

    Solution :

               \[v=\frac{c\Delta \lambda }{\lambda }=\frac{3\times {{10}^{8}}\times (706-656)}{656}=\frac{1500}{656}\times {{10}^{7}}\] \[=2\times {{10}^{7}}m/s\]


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