Ray Optics

JEE Main level, single correct, medium

225 of 295

Question 225 of 295

A thin convex lens LL (refractive index =1.5=1.5 ) is placed on a plane mirror MM. When a pin is placed at AA, such that OA=18cm,OA=18cm, its real inverted image is formed at AA itself, as shown in figure. When liquid of refractive index μl{\mu }_{l} is put between the lens and the mirror, the pin has to be moved to A′,{A}^{'}, such that OA′=27cm,O{A}^{'}=27 cm, to get its inverted real image at A′A' itself. The value of μl{\mu }_{l} will be

Show answer and solution

Answer: (A) 43\dfrac{4}{3}

1f1=12×218\dfrac{1}{{f}_{1}}=\dfrac{1}{2}\times \dfrac{2}{18}
1f2=(μ1−1)−18\dfrac{1}{{f}_{2}}=\dfrac{\left({\mu }_{1}-1\right)}{-18}
When μ1{\mu }_{1} is filled between lens and mirror,
P=218−218(μ1−1)=2−2μ1+218P=\dfrac{2}{18}-\dfrac{2}{18}\left({\mu }_{1}-1\right)=\dfrac{2-2{\mu }_{1}+2}{18}
⇒Fm=−(182−μ1)\Rightarrow {F}_{m}=-\left(\dfrac{18}{2-{\mu }_{1}}\right)
2=6−3μ12=6-3{\mu }_{1}
3μ1=43{\mu }_{1}=4
μ1=43{\mu }_{1}=\dfrac{4}{3}

JEE Main question paper PDF

Open a shift to read the full paper on this page, or download it.

JEE Main 2025 Apr 2 Shift 1 question paper

Open Download PDF

Opening paper…

Explain it as a whiteboard videoStep-by-step, in Hinglish or English. Your first video needs no login.Solved it on paper but got it wrong?Upload a photo of your working. Mistake Doctor marks the exact line that broke.
See it move: Lens ray diagram simulationDrag the sliders and watch the numbers in this question change.Revise Ray Optics firstFormula sheet, solved examples and the traps students fall into.

More Physics practice

JEE Main Physics practice question on Ray Optics (Combination of Lens and Mirrors), with the answer and a step-by-step solution. Scan a question from your own book or paper to get a whiteboard video.