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Question
A converging mirror forms a real image of height 4 cm of an object of height 1 cm placed 20 cm away from the mirror : (1) Calculate the image distance. (ii) What is the focal length of the mirror ?
A converging mirror forms a real image of height 4 cm of an object of height 1 cm placed 20 cm away from the mirror : (1) Calculate the image distance. (ii) What is the focal length of the mirror ?
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Solution
Given that
Height of object, h = 1 cm
Height of image, h'= -4 cm
Object distance, u = -20 cm
Now,
Magnification, m = -v/u = h'/h
=> v/20 = -4/1
=> v = -80 cm
This is the image distance.
Now,
1/f = 1/v + 1/u
=> 1/f = -1/80 – 1/20
=> f = -16 cm
This is the focal length of the mirror.
Given that
Height of object, h = 1 cm
Height of image, h'= -4 cm
Object distance, u = -20 cm
Now,
Magnification, m = -v/u = h'/h
=> v/20 = -4/1
=> v = -80 cm
This is the image distance.
Now,
1/f = 1/v + 1/u
=> 1/f = -1/80 – 1/20
=> f = -16 cm
This is the focal length of the mirror.
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