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प्रश्न
At what distance from a concave mirror of focal length 10 cm should an object be placed so that:
its real image is formed 20 cm from the mirror?
उत्तर
Given
It is a concave mirror.
f=-10 cm
v=-20 cm
Since the image is real and forms in front of the mirror, the equation will be `1/f=1/v+1/u`
`1/-10=1/-20+1/u`
`2/u=1/-10+1/20`
`1/u=(-20+10)/200`
`1/u = (-10)/200`
`1/u=-1/20`
u=-20 cm
Therefore, the object should be placed at a distance of 20 cm from the mirror to form a real image.
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