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Question
An object 3 cm high is placed at a distance of 8 cm from a concave mirror which produces a virtual image 4.5 cm high:
(i) What is the focal length of the mirror?
(ii) What is the position of image?
(iii) Draw a ray-diagram to show the formation of image.
Solution
Distance of the object from the mirror 'u' = -8 cm
Height of the object 'ho' = 3 cm
Height of the image 'hi' = 4.5 cm
We have to find the focal length of the mirror 'f' and distance of the image 'v'.
Using the magnification formula, we get
`m=h_i/h-o=-v/u`
`m4.5/3=(-v)/(-8)`
`v=4.5xx8/3=12`cm
Therefore, the distance of the image 'v' is 12 cm behind the mirror.
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