Power \((P)\)
Refractive index is assume \(\left(\mu_{\ell}\right)\)
\(P =\frac{1}{ f }=\left(\mu_{\ell}-1\right)\left(\frac{2}{ R }\right)\) \(...(i)\)
\(P ^{\prime}=\frac{1}{ f ^{\prime}}=\left(\mu_{\ell}-1\right)\left(\frac{1}{ R ^{\prime}}\right)\)\(....(ii)\)
\(P ^{\prime}=\frac{3}{2} P\)
\(\left(\mu_{\ell}-1\right)\left(\frac{1}{ R ^{\prime}}\right)=\mu \frac{3}{2}\left(\mu_{\ell}-1\right)\left(\frac{2}{ R }\right)\)
\(\therefore \quad R ^{\prime}=\frac{ R }{3}\)