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An object is placed 40 cm in front of a concave mirror of focal length 20cm. A plane mirror is placed at a distance of 20 cm in front of the concave mirror. Find the final position of the image.

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1 Answer

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f= Focal length of concave mirror =20cm

d= Distance of object from concave mirror = 40cm

di = Distance of image  from concave mirror = ?

According to concave mirror formula 

1/f = 1/d + 1/di

So,  1/d= 1/f  -  1/d

             = 1/20 - 1/40    = 1/40

Thus, di   = 40cm in front of the concave mirror.

But , a plane mirror is palced  at a distance of 20cm,  so image rays after reflection from plane mirror goes to concave mirror and formed image at Infinity. Since Image formed of object placed  at focus is infinity.

The final position of the image is infinity

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