JEE Main 2015 · 11 Apr · Shift 1 · Physics Q24

← JEE Main 2015 · 11 Apr · Shift 1

PhysicsSingle correct+4 / -1Question 24 of 90

A thin convex lens of focal length 'f' is put on a plane mirror as shown in the figure. When an object is kept at a distance 'a' from the lens - mirror combination, its image is formed at a distance $\dfrac a3$ in front of the combination. The value of 'a' is :

A thin convex lens resting against a vertical plane mirror (hatched), with the axis dashed.

\dfrac32f

Answer and worked solution

Official answer: B

The lens-mirror combination acts as a concave mirror of focal length $\frac f2$ . With $u=-a$ and $v=-\frac a3$ :
$\frac1v+\frac1u=-\frac3a-\frac1a=-\frac2f\implies a=2f.$

Topics:Combination of lenses and mirrors

← Previous question Next question →

JEE Main 2015 · 11 Apr · Shift 1, Physics question 24