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प्रश्न
At what distance from a concave mirror focal length 10 cm should an object 2 cm long be placed in order to get an erect image 6 cm tall?
उत्तर
Height of the object 'ho' = 2 cm
Focal length of the mirror 'f' = −10 cm
Height of the image 'hi' = 6 cm
We have to find the distance of the object from the mirror 'u'.
Using the magnification formula, we get
`m= h_i/h_o=-v/u`
`m=6/2=-v/u`
`m=3=-v/u`
thus v=-3u
Now, using the mirror formula, we get
`1/f=1/v+1/u`
`1/-10=1/(-3u)+1/u`
`1/10=1/(3u)-3/(3u) =(-2)/(3u)`
`u=(-2xx10)/3`
u=-6.67 cm
Thus, the distance of the object from the mirror 'u' is −6.67 cm.
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