IIT-JEE 2010 · Paper 2, Physics question 56

In every figure the ray comes from $\mu_1$ (right), crosses the lens ($\mu_2$) and leaves into $\mu_3$ (left).

Reading each diagram.

• P (biconvex): bends towards the axis at the first surface (converging, so $\mu_2>\mu_1$ for a convex face) and is undeviated at the second ($\mu_2=\mu_3$).
• Q (convex face first, then plane): bends away from the axis at the convex face (so $\mu_1>\mu_2$), and further away at the plane face (the ray, already inclined, goes into a rarer medium: $\mu_2>\mu_3$).
• R (biconcave): bends away from the axis at the first, concave surface (diverging, so $\mu_2>\mu_1$) and is undeviated at the second ($\mu_2=\mu_3$).
• S (concave face first, then plane): bends towards the axis at the concave face (a concave surface converges when $\mu_1>\mu_2$), and bends further at the plane face ($\mu_2>\mu_3$).
• T (biconcave): bends strongly towards the axis at the first surface ($\mu_1>\mu_2$) and is undeviated at the second ($\mu_2=\mu_3$).

Matching.

• A ($\mu_1<\mu_2$): P, R.
• B ($\mu_1>\mu_2$): Q, S, T.
• C ($\mu_2=\mu_3$): P, R, T.
• D ($\mu_2>\mu_3$): Q, S.

Answer: A → P, R; B → Q, S, T; C → P, R, T; D → Q, S