b
લેન્સ મેકસના સુત્ર પ્રમાણે \(\,\frac{1}{{f}}\,\, = \,\,(\mu  - 1)\,\,\left[ {\frac{1}{{{R_1}}} - \frac{1}{{{R_2}}}} \right]\) સાથે \(\mu \,\, = \,\,\frac{{{\mu _L}}}{{{\mu _M}}}\)

અહીં \( {f}\,\, = \,\,30  cm,\,\, {R_1} = \,\,10\,\,\,cm\,\) અને  \({R_2} = \,\,\infty \,\,\,\,\,\frac{1}{{30}}\,\,\)

\( = \,\,\,(\mu  - 1)\,\,\left[ {\frac{1}{{10}} - \frac{1}{\infty }} \right]\,\,\,\,\, \Rightarrow \,\,\,3\mu  - 3\,\, = \,\,1\,\,\,\,\, \Rightarrow \,\,\,\,\mu \, = \,\,\frac{4}{3}\)