The focal length of a thin biconvex lens is 20 cm. When an object is moved from a distance of 25 cm in front of it to 50 cm, the magnification of its image changes from m25 to m50. The ratio is

Engineering

Physics

Curved Surface Refraction

Question

The focal length of a thin biconvex lens is 20 cm. When an object is moved from a distance of 25 cm in front of it to 50 cm, the magnification of its image changes from m₂₅ to m₅₀. The ratio $\frac{m_{25}}{m_{50}}$ is

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$\frac{1}{v} - \frac{1}{u} = \frac{1}{f}$

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

$\frac{u}{v} = (\frac{f + u}{f})$

$m = (\frac{u}{v}) = (\frac{f}{f + u})$

$m_{25} = \frac{20}{20 - 25} = - 4$

$m_{50} = \frac{20}{20 - 50} = \frac{- 2}{3}$

$\frac{m_{25}}{m_{50}} = \frac{- 4}{- 2 / 3} = 6$