Question

A converging lens of focal length 5 cm is placed at a distance of 20
cm from a screen. How far from the lens should an object be placed so
as to form its real image on the screen ?

Answer 1

The object be should be placed 6.67cm from the lens so as to form its real image on the screen.

How can we calculate the distance?

f is given as +5cm

v is given as +20cm

Since we are dealing with real image then /u/ > F/

Then, 1/f = 1/v -1/u

if we substitute the values we have,

1/u = 1/20 -1/5

then u= -6.67cm

Therefore, object be should be placed 6.67cm from the lens so as to form its real image on the screen.

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