A concave mirror of radius of curvature 30 cm produces a real image 3 times the size of an object. Find object distance?
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Given :
Radius of curvature = 30cm
Image size = 3 times
To find:
The distance between object and image.
Solution :
As radius of curvature of concave mirror is 30cm
therefore, focal length of concave mirror, f = -R/2 = -30/2 = -15 cm
As real image is three times the size of the object,
thus magnification, m = - 3
= -v/u = -3
= v = 3u --- eq 1
Lens formula, 1/v + 1/u = 1/f
= 1/3u + 1/u = 1/-15
= 4/3u = 1/-15
= u = - 20 cm
v = 3u = 3 × -20
= - 60
Distance between the object and the image 60 - 20 = 40
Answer: The object distance is 40cm
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