1.

A convex lens produces a real and inverted image 2.5 times maganified at a distance of 25 cm from the lens. Calcuate the focal length of the lens.

Answer»

SOLUTION :Given : Magnification = 2.5 (Real image)
Distance ofthe image (v) = 25 cm
To find :
Distance of the object (u)
Focal LENGTH (f)
Solution : M = `(h_(2))/(h_(1))`
-2.5 =` 25/(h_(1)) `
`h_1 = -10`
`therefore` Distance of the object = 10 cm .
`1/v - 1/u = 1/f `
`1/25 - 1/-10 = 1/f `
`1/25 + 1/10 = 1/f `
`1/f = (2+5)/50`
`1/f = 7/50`
`f = 50/7 `
f = 7.14 cm


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