Question
Physics Question on Ray optics and optical instruments
A bi-convex lens is formed with two thin plano-convex lenses as shown in the figure. Refractive index n of the first lens is 1.5 and that of the second lens is 1.2. Both the curved surfaces are of the same radius of curvature R=14cm.For this bi-convex lens, for an object distance of 40cm, the image distance will be
A
−280.0cm
B
40.0cm
C
21.5cm
D
13.3cm
Answer
40.0cm
Explanation
Solution
Using the lens formula,
v1−u1=F1=f11+f21
or v1=u1+f11+f21
15mm=u1+(n1−1)(R11−R21)+(n2−1)(R1′1−R2′1)
Substituting the values, we get
v1=−401+(1.5−1)(141−81)+(1.2−1)(81−141)
Solving this equations, we get
v=+40cm