Ray Optics Question 9
Question 9 - 2024 (30 Jan Shift 2)
In an experiment to measure the focal length (f) of a convex lens, the magnitude of object distance (x) and the image distance (y) are measured with reference to the focal point of the lens. The $y-x$ plot is shown in figure.
The focal length of the lens is $\mathrm{cm}$.
Show Answer
Answer: (20)
Solution:
$\frac{1}{\mathrm{f}+20}-\frac{1}{-(\mathrm{f}+20)}=\frac{1}{\mathrm{f}}$
$\frac{2}{\mathrm{f}+20}=\frac{1}{\mathrm{f}} \quad \mathrm{f}=20 \mathrm{~cm}$
Or $\mathrm{x}{1} \mathrm{x}{2}=\mathrm{f}^{2}$ gives $\mathrm{f}=20 \mathrm{~cm}$
