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Question
When an object is placed at a distance of 15 cm from a concave mirror, its image is formed at 10 cm in front of the mirror. Calculate the focal length of the mirror.
Solution
Distance of the object from the mirror 'u' = −15 cm
Distance of the image 'v' = −10 cm
We have to find the focal length of the mirror 'f'.
Using the mirror formula, we get
`1/f=1/v+1/u`
`1/f=1/(-10)+1/(-15)=-1/10-1/15`
`1/f=-3/30-2/30`
`1/f=-5/30`
f=-6 cm
Thus, the focal length of the concave mirror 'f' is 6 cm.
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