A) - 60 cm
B) + 60 cm
C) -120 cm
D) + 120cm
Correct Answer: C
Solution :
The condition for achromatism is \[\frac{{{\omega }_{1}}}{{{\omega }_{2}}}=-\frac{{{f}_{1}}}{{{f}_{2}}}\] or \[{{f}_{1}}=-\frac{{{\omega }_{1}}}{{{\omega }_{2}}}{{f}_{2}}\] \[\therefore \] \[{{f}_{1}}=-\frac{0.066}{0.033}\times 60=-120\,cm\]You need to login to perform this action.
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