1.

A lens of focal length 5 cm is being used by a student in the laboratory as a magnifying glass. His least distance of distinct vision is 25 cm. What magnification is the student getting?

Answer»

Solution :Given, image distance = v = -25 cm, focal length = f = 5 cm, magnification = m = ?
From LENS formula, `(1)/(f) = (1)/(v) - (1)/(u) = (1)/(u) = (1)/(v) - (1)/(f)`
`(1)/(u) = (1)/(-25)-(1)/(5) = (-1-5)/(25) = (-6)/(25)`
Object distance `= u = (-25)/(6) cm`.
We know that, `m = (v)/(u) = (-25 - 6)/(-25) = 6`.


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