• # question_answer The frequency of a wave of light is $12\times {{10}^{14}}{{s}^{-1}}.$ The wave number associated with this light is         [Pb. PMT 1999] A)                 $5\times {{10}^{-7}}m$               B)                 $4\times {{10}^{-8}}c{{m}^{-1}}$ C)                 $2\times {{10}^{-7}}{{m}^{-1}}$              D)                 $4\times {{10}^{4}}c{{m}^{-1}}$

Frequency $\nu =12\times {{10}^{14}}{{s}^{-1}}$ and velocity of light $c=3\times {{10}^{10}}cm\,{{s}^{-1}}$. We know that the wave number $\overline{\nu }=\frac{v}{c}=\frac{12\times {{10}^{14}}}{3\times {{10}^{10}}}=4\times {{10}^{4}}c{{m}^{-1}}$