A screen is placed 90 cm from an object. The image of the object on the screen is formed by a convex lens at two different locations separated by 20 cm. Determine the focal length of the lens.

Solution

Here,
Distance between object and screen, D = 90 cm
Distance between two locations of convex lens, d = 20 cm
Since,
Focal length of the lens is, $f = \frac{D^{2} - d^{2}}{4 D}$

$∴$ $f = \frac{(90)^{2} - (20)^{2}}{4 \times 90} = \frac{(90 + 20) (90 - 20)}{360} = \frac{110 \times 7}{36}$

$\Rightarrow$ $f = 21.4 cm .$

For Daily Free Study Material Join wiredfaculty

Wave Optics

A screen is placed 90 cm from an object. The image of the object on the screen is formed by a convex lens at two different locations separated by 20 cm. Determine the focal length of the lens.

Some More Questions From Wave Optics Chapter

Mock Test Series

NCERT Sample Papers

Entrance Exams Preparation

Phone Number

Email Address

Loaction