Question 2: An object is placed (a) 20 cm, (b) 4 cm, in front of a concave mirror of focal length 12 cm. Find the nature and position of the image formed in each case.
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a) u = - 20 cm, f = -12 cm
1/v + 1/u = 1/f
1/v + 1/-20 = 1/-12
1/v = -1/12 + 1/20 = (-20 + 12)/240 = -8/240
V = - 30 cm
The image is formed at a distance of 30 cm in front of the mirror.
The image is real and inverted.
(b) u = - 4 cm, f = -12 cm
1/v + 1/u = 1/f
1/v + 1/-4 = 1/-12
1/v = -1/12 + 1/4 = (-1 + 3)12 = 2/12
V = 6 cm
The image is formed at a distance of 6 cm behind the mirror.
The image is virtual and erect.
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