A convex mirror of focal length `20 cm` is placed `50 cm` from a wall. How far the wall should an object be placed to form a real image on the wall ?
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Here, `f = -20 cm, v = -50 cm` Let the object `AB` be held at a distance `x` from the wall, Image `A'B'` is formed on the wall. `u = -(50 - x)cm` From `(1)/(v) + (1)/(u) = (1)/(f)` `(1)/(u) = (1)/(f) - (1)/(v) = (1)/(-20) - (1)/(-50) = (-5 + 2)/(100)` `u = -(100)/(3)cm = -33.3 cm` As `u = -(50 - x) = -33.3` `x = 50 - 33.3 = 16.7 cm`
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