Verified Solution • 2025–26 Session moderate

QJEEM20Ph5dbd: JEE Main 2020 Physics - Class 12 JEEM20Ph5dbd Solution: The distance between an object and a screen is 100 cm. A lens…

The distance between an object and a screen is 100 cm. A lens can produce real image of the object on the screen for two different positions between the screen and the object. The distance between these two positions is 40 cm. If the power of the lens is close to (N100)D\left( {{N \over {100}}} \right)D where N is an integer, the value of N is _________.

Step-by-Step Verified Solution

Using displacement method

f=D2−d24Df = {{{D^2} - {d^2}} \over {4D}}

Here, D = 100 cm

and d = 40 cm

f=1002−4024(100)=21 cmf = {{{{100}^2} - {{40}^2}} \over {4(100)}} = 21\,cm

P=1f=10021DP = {1 \over f} = {{100} \over {21}}D

N100=10021{N \over {100}} = {{100} \over {21}}

N=476N = 476

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