Answer:
[tex]R_2 = 1.86 cm[/tex]
Explanation:
By lens makers formula we know that focal length is given as
[tex]\frac{1}{f} = (\frac{\mu_2}{\mu_1} - 1)(\frac{1}{R_1} - \frac{1}{R_2})[/tex]
now we know that
[tex]\mu_1 = 1[/tex]
[tex]\mu_2 = 1.38[/tex]
[tex]R_1 = 0.5 cm[/tex]
f = 1.80 cm
now from above expression
[tex]\frac{1}{1.80} = (1.38 - 1)(\frac{1}{0.5} - \frac{1}{R_2})[/tex]
[tex]R_2 = 1.86 cm[/tex]