Answers

2016-03-17T20:24:54+05:30
If we know the image distance and object distance then we can find focal length

 \frac{1}{f} =  \frac{1}{v} + \frac{1}{u}

where u = object distance
v = image distance

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2016-03-17T20:34:57+05:30
1 Hold a concave mirror and direct its reflecting surface towards the sun
2 direct the sunlight on a sheet of paper to obtain a sharp image
3 distance between mirror and sheet of paper gives approximate focal length of mirror
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