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  • An experiment is conducted to determine the focal length (f) of a convex lens using the lens formula. An object is placed at a distance u = 20 cm from the lens, and its image is formed on a screen

An experiment is conducted to determine the focal length (f) of a convex lens using the lens formula. An object is placed at a distance u = 20 cm from the lens, and its image is formed on a screen at a distance v = 40 cm from the lens. Calculate the focal length of the convex lens.

Option: 1

16.67 cm


Option: 2

13.33 cm


Option: 3

20 cm


Option: 4

23 cm


Answers (1)

Given values:

Object distance (u) = 20 cm
Image distance (v) = 40 cm

The lens formula relates the object distance, image distance, and focal length (f) of a lens:

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

Step 1: Substitute the given values into the lens formula:

                    \frac{1}{f} = -\frac{1}{-20 cm} + \frac{1}{40 cm}

Step 2: Solve for the focal length f:

                    f = \frac{1}{\frac{1}{20 cm} + \frac{1}{40 cm}}

Step 3: Calculate the sum in the denominator:

                    f = \frac{1}{\frac{2+1}{40 cm}}

Step 4: Calculate the reciprocal of the sum:

                    f = \frac{40 cm}{3}

Step 5: Calculate the focal length f:

                    f = 13.33 cm

The focal length of the convex lens is 13.33 cm.

Posted by

Sumit Saini

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