1. An object of height 1.2m is placed before a concave mirror of focal length 20 cm so that a real image is formed at a distance of 60cm from it. Find the position of an object. What will be the height of the image formed?
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As it is a concave mirror, focal length and image distance should be negative. So, by mirror formula we get the object distance =(-30cm). And by magnification formula - v/u we get m=(-2) and after find height of image by magnification.
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height of object=1.2m
focal length of concave mirror=-20cm
v=60cm
we know that ,1/f=1/u+1/v
therefore ,1/u=1/f-1/v
1/u=1/-20-1/60
1/u=1/20+1/60=4/60=1/15
U=-15
therefore position of object=-15cm
(2) what will be the height of image
we know that,
height of image/height of object= -v/u
height of image/120cm=-60/-15
height of image = 480 cm
focal length of concave mirror=-20cm
v=60cm
we know that ,1/f=1/u+1/v
therefore ,1/u=1/f-1/v
1/u=1/-20-1/60
1/u=1/20+1/60=4/60=1/15
U=-15
therefore position of object=-15cm
(2) what will be the height of image
we know that,
height of image/height of object= -v/u
height of image/120cm=-60/-15
height of image = 480 cm
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