size of image of an object by a mirror having a focal length of 20cm is observed to be reduced to1\3rd of its size at what distance the object has been placed from the mirror? what is the nature of the image and the mirror?
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Step-by-step explanation:
HII!
lets see the answer in cases!1
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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