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The dispersive power of the material of a lens is `0.04` and the focal length of the lens is `10cm`. Find the difference in the focal length (in mm) of the lens for violet and red colour. |
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Answer» Correct Answer - 4 `1/f=(n-1)(1/(R_(1))-1/(R_(2)))implies-(df)/(f^(2))implies-(df)/(f^(2))=(1/(R_(1))-1/(R_(2)))dn` (differentiating both sides) `implies-(df)/f(n-1)(1/(R_(1))-1/(R_(2)))=(1/(R_(1))-1/(R_(2)))dn` `=-df=f(dn)/(n-1)` but `dn-v_(v)-n_(R):.-df=(n_(v)-n_(R))/(n-1)f` `impliesdf=-wfimpliesf_(v)-f_(R)=-wf` `=-0.04xx10=0.4cm` `f_(R)-f_(v)=4mm` |
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