A screen is placed 90 ; cm from an object. Th | vedclass

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(A) The distance between the object and the screen is $D = 90 \; cm$.The distance between the two positions of the lens is $d = 20 \; cm$.The focal le

Vedclass · Accepted Answer

$21.4$

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(A) The distance between the object and the screen is $D = 90 \; cm$.The distance between the two positions of the lens is $d = 20 \; cm$.The focal length $f$ of the convex lens is given by the displacement method formula:$f = \frac{D^2 - d^2}{4D}$Substituting the given values:$f = \frac{(90)^2 - (20)^2}{4 	imes 90}$$f = \frac{8100 - 400}{360}$$f = \frac{7700}{360}$$f = \frac{770}{36} \approx 21.39 \; cm$.Rounding to one decimal place,the focal length is $21.4 \; cm$.

$A$ 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 (in $cm$) of the lens.

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