Question

5. A concave mirror of focal length 20 cm forms an image having twice the size of object. For the
virtual position of image, the position of object will be at
(0/1 Point)
ta) 25 cm
D) 40 cm
(C) 30 cm
{d) less than 20 cm

Answer 1

Answer:  

Focal length of concave mirror = f = 20 cm

Magnification = m = 2  

m = (–v / u)  

∴ 2 = (–v / u)  

Hence v = –2 u ...(1)  

Also (1/f) = (1/v) + (1/u)  

∴ (1/f) = (1 / –2 u) + (1/u)  

(1/f) = {(– 1 + 2) / (2 u)} = (1 / 2 u)  

∴ 20 = 2 u  

u = 10 cm i.e. position of object is 10 cm.

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