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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3
Answer:
Explanation:
f = 20
m = 1/3
-v/u = 1/3
-3v = u
1/f = 1/v + 1/u
1/20 = 1/v - 1/3v
1/20 = ( 3-1 )/3v
1/20 = 2/3v
20 = 3v/2
40 = 3v
v = 40/3
v = 13.33
the mirror is a convex mirror
Answered by
0
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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