How far should an object be from pole of a concave mirror of focal length 20 cm to form a real image whose size is 1 5th of the size of the object<br />
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Given,
f = -20cm
Image distance (v)
Object distance (u)
Magnification,m is given as,
m = I/O = – v/u ( ratio of size of image to size of object which is equal to ratio of image distance to object distance)
1/5 = – v/u
or, v = – u/5
now applying the mirror formula,
1/f = 1/u + 1/v
– 1/20 = 1/u – 5/u
1/20 = 1/u + 5/u as image is real so v will be negative so on putting its value it becomes positive
or, u= – 120cm