An object 1 cm high is placed at a distance of 1.5 m from the screen. How far a concave mirror be placed so that it may form a 2cm high image of the object on the screen? Also find the focal length of the mirror.

since image is larger than object so its image is virtual ...

let the mirror is placed at u distance far from object & v distance far from screen...     (mirror is bw object & screen)

v/u = 2/1 = 2

v = 2u                   (given)

v + u = 1.5           

u = 1.5/3 = -50cm

v = 100

focal length = f

applying lens formula

1/v + 1/u =1/f

-1/50 + 1/100 = 1/f

f = -100cm

thus mirror should be placed at a distance 100cm from screen...

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