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Q. 1. A concave mirror of focal length 20em is placed 50 cm from a wall. How far from the wall an object beplaced to form its real image on the wall?

Answer»

We are given a concave mirror.

Object distance= u

Image distance, v = - 50 cm

Focal length = f=-20cm

Now,

1/f = 1/v + 1/u

-1/20=-1/50+1/u

1/u=1/50-1/20=-3/100

u=-100/3=-33.3cm

This is the distance of object from mirror,now distance of the object from the wall=-50-(-33.3)=-16.7cm

i.e 16.7cm left of the mirror.



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