A transparent thin film of uniform thickness and refractive index $n subscript 1 end subscript equals 1.4$ is coated on the convex spherical surface of radius R at one end of a long solid glass cylinder of refractive index $n subscript 2 end subscript equals 1.5$ , as shown in figure. Rays of light parallel to the axis of the cylinder traversing through the film from air to glass get focused at distance f₁ from the film, while rays of light traversing from glass to air get focused at distacnce f₂ from the film. Then

$|f_{1}| = 3 R$
$|f_{1}| = 2.8 R$
$|f_{2}| = 2 R$
$|f_{2}| = 1.4 R$