Question 2: Ray Optics

Question

Calculate the focal length of given lens if the
magnification is $$-$$0 5.

Accepted Answer

From figure,
Distance of object, $$u=-20 \mathrm{~cm}$$
Magnification, $$m=-0.5$$
Magnification of lens in terms of $$u$$ and $$f$$ is given by
$$\begin{aligned}
m & =\frac{f}{u+f} \
-0.5 & =\frac{f}{-20+f} \
\Rightarrow \quad 10-0.5 f & =f \Rightarrow 1.5 f=10 \
f & =\frac{10}{1.5} \
f & =6.66 \mathrm{~cm}
\end{aligned}$$

Answer

6.66 cm

Answer

5.44 cm

Answer

3.88 cm

Answer

1.38 cm

Ray Optics

Calculate the focal length of given lens if the magnification is $-$0 5.

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