A ray of light starting from O gets refracted twice. The ray of light is travelling in a direction from left to right. Hence, the distance measured in this direction are taken positive.Applying
µ2
v
−
µ1
u
=
µ2−µ1
R
, twice with proper signs. We have,
3
2
v
−
4
3
−20
=
3
2
−
4
3
10
Or v=−30cm Now, the first image I1 acts as an object for the second surface, where BI1=u=−(30+20)=−50cm
4
3
v
−
3
2
−50
=
4
3
−
3
2
−10
∴v1=−100cm, i.e., the final image I3 is virtual and is formed at a distance of 100 cm(towards left) from B.