Question 283: Ray Optics

Question

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 ________ $$\mathrm{cm}$$.

Accepted Answer

$$\begin{aligned}
& \frac{1}{f+20}-\frac{1}{-(f+20)}=\frac{1}{f} \
& \frac{2}{f+20}=\frac{1}{f} \quad f=20 \mathrm{~cm}
\end{aligned}$$
Or $$\mathrm{x}_1 \mathrm{x}_2=\mathrm{f}^2$$ gives $$\mathrm{f}=20 \mathrm{~cm}$$

Ray Optics

In an experiment to measure the focal length $(f) of a convex lens, the magnitude of object distance (x) and the image distance (y) are measured with reference to the focal point of the lens. The y-x plot is shown in figure. The focal length of the lens is ________ \mathrm{cm}$.

Choose the correct answer: