Join the Most Relevant JEE Main 2025 Test Series & get 99+ percentile! Join Now
Search any question & find its solution
Question: Answered & Verified by Expert
In a concave mirror, an object is placed at a distance $d_1$ from the focus and the image is formed at a distance $d_2$ from the focus. Then the focal length of the mirror is
PhysicsRay OpticsAIIMSAIIMS 2009
Options:
  • A $\sqrt{d_1 d_2}$
  • B $d_1 d_2$
  • C $\left(d_1+d_2\right) / 2$
  • D $\sqrt{d_1 / d_2}$
Solution:
1002 Upvotes Verified Answer
The correct answer is: $\sqrt{d_1 d_2}$
$\mathrm{U} \operatorname{sing} \frac{1}{v}+\frac{1}{u}=\frac{1}{f}$
Given $u=f+d_1 \quad v=f+d_2$
$f=\frac{u v}{u+v}=\frac{\left(f+d_1\right)\left(f+d_2\right)}{\left(f+d_1\right)+\left(f+d_2\right)}$
On solving $f=\sqrt{d_1 d_2}$

Looking for more such questions to practice?

Download the MARKS App - The ultimate prep app for IIT JEE & NEET with chapter-wise PYQs, revision notes, formula sheets, custom tests & much more.