Question

If the optical axis of convex and concave lenses are separated by a distance 5mm shown in the figure. If the coordinates of final image formed by the combination of lenses is (x, y) when the parallel beam of light is incident on convex lens. If origin is at the optical centre of convex lens, $\frac{x}{20y}$ = ___.

Answer 1

By convex lens v = +20 cm

For concave lens u = –10 cm

$\frac{1}{v}-\frac{1}{-10}=\frac{1}{-10}$

$v=-5cm$

So, x-coordinate is (30 – 5) cm = 25 cm

$m=\frac{v}{u}=\frac{h_I}{5mm}\Rightarrow h_i=2.5mm=0.25cm$

So, y-coordinate is + 0.25 cm