QQuestion
A convex lens of focal length 10 cm is placed at a distance of 60 cm from a screen. How far from the lens should an object be placed so as to obtain a real image on the screen?
✓Answer
Given, focal length, f = 10 cm
Image distance, v = 60 cm
Object distance, u = ?
Lens formula: \frac{1}{v}-\frac{1}{u}=\frac{1}{f}
Substituting the values:
\frac{1}{60}-\frac{1}{u}=\frac{1}{10} -\frac{1}{u}=\frac{1}{10}-\frac{1}{60}=\frac{5}{60}=\frac{1}{12} u=-12\,\text{cm}Therefore, the object should be placed 12 cm in front of the lens.
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