An air bubble in a glass sphere having 4 cm diameter appears 1 cm from surface nearest to eye when looked along diameter. If µ_g = 1.5, the distance of bubble from refracting surface is

1.2 cm

By using $\frac{\mu_2}{v}-\frac{\mu_1}{u}=\frac{\mu_2-\mu_1}{R}$

where u = ?,  v = -1 cm,  $\mu_1$ = 1.5,  $\mu_2$ = 1 ,  R = -2 cm

$\frac{1}{-1}-\frac{1.5}{u}=\frac{1-1.5}{(-2)} \quad \Rightarrow \quad u=-\frac{6}{5}$ = -1.2 cm