[tex]\text{Distanta focala a unei lentile (subtiri) este }\\
\boxed{f=\dfrac{1}{(n-n_1)\left(\frac{1}{R_1}-\frac{1}{R_2}\right)}}\\
\text{Atunci cand se afla in vid(sau aer) distanta focala este:}\\
f_1=\dfrac{1}{(1,5-1)\left(\frac{1}{R_1}-\frac{1}{R_2}\right)} =\dfrac{2}{\frac{1}{R_1}-\frac{1}{R_2}}\\
\text{Dupa ce lentila este introdusa in lichid,distanta focala devine :}\\
f_2=\dfrac{1}{(1,5-1,2)\left(\frac{1}{R_1}-\frac{1}{R_2}\right)} =\dfrac{10}{3\left(\frac{1}{R_1}-\frac{1}{R_2}\right)}[/tex][tex]\text{Impartim cele doua rezultate si obtinem:}\\
\dfrac{f_1}{f_2}=\dfrac{2}{\frac{10}{3}}=\dfrac{6}{10}=\dfrac{60}{100}\\
f_1=\dfrac{60}{100}\cdot f_2
[/tex]
