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  • An experiment is conducted to determine the focal length  of a concave lens using a lens formula. The object dist

An experiment is conducted to determine the focal length (f) of a concave lens using a lens formula. The object distance (u) is 25\ cm, and the image distance (v) is 40\ cm. Calculate the focal length of the concave lens.

Option: 1

-15.385\ cm


Option: 2

13.245\ cm


Option: 3

-16.355\ cm


Option: 4

10.685\ cm


Answers (1)

best_answer

Given values:
• Object distance (u)=25\ cm
• Image distance (v)=40\ cm
The lens formula relates the object distance, image distance, and focal
length:

\frac{1}{f}=-\frac{1}{u}+\frac{1}{v}

Solve for the focal length (f):
f=\frac{u v}{u-v}
Step 1: Calculate the focal length (f):
f=\frac{-25 \mathrm{~cm} \times-40 \mathrm{~cm}}{-25 \mathrm{~cm}-40 \mathrm{~cm}}

Step 2: Calculate f:

\begin{aligned} & f=\frac{1000 \mathrm{~cm}^2}{65 \mathrm{~cm}} \\ & f-15.385 \mathrm{~cm} \end{aligned}

The focal length of the concave lens is approximately -15.385\ cm
Therefore, the correct option is (A).

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