Question

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Practice Problem : 1
1. An object 3 cm high produces a real image 4.5 cm high, when placed at a distance of
20 cm from a concave mirror. Calculate : (i) the position of image (ii) focal length
of the concave mirror.
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Answer 1

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Answer 2

Answer:

Here

object height h1=3cm

image height h2=4.5cm

we know

m=h2/h1=-v/u

so,

4.5/3=-v /-20 (object distance =20)

4.5×-20/3=-v

v=30cm

so image is 30 cm from the mirror.

now , using mirror formula

1/u+1/v=1/f

1/-20+1/-30=1/f

-5/60=1/f

-1/12=1/f

f=-12

Hence , the required focal length is 12cm

Explanation:

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