size of image of an object by a mirror having a focal length 20 cm is observed to be reduce to 1/3 of its size . at what distance from the mirror the object has been placed and what is nature of image and the mirror.
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CASE 1:- m=-1/3(in case of concave mirror)
f= -20 cm
m= -1/3 =-v/u
v=u/3
1/f= 1/v +1/u .
=> -1/20 = 3/u + 1/ u= 4/u
therefore.,, u = -80 cm.
CASE 2:-
M=+1/3 (IN CASE OF CONVEX MIRROR)
f=+20 cm.
m=+1/3 =-v/u
v=-u/3.
i/f=1/v+1/u.
=> 1/20= -3/4 + 1/4 =-2/4
therefore, u= -40 cm.
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