QuestionMay 25, 2025

A converging lens has a focus length of 20 cm. A pencil stands on its optic axis with a distance of 30 cm from the lens. What is the image distance? A) 45 cm B) 10 cm C) 60 cm

A converging lens has a focus length of 20 cm. A pencil stands on its optic axis with a distance of 30 cm from the lens. What is the image distance? A) 45 cm B) 10 cm C) 60 cm
A converging lens has a focus length of
20 cm. A pencil stands on its optic axis
with a distance of 30 cm from the lens.
What is the image distance?
A) 45 cm
B) 10 cm
C) 60 cm

Solution
4.3(233 votes)

Answer

C) 60 cm Explanation 1. Use Lens Formula Apply the lens formula \frac{1}{f} = \frac{1}{d_o} + \frac{1}{d_i}, where f = 20 cm and d_o = 30 cm. 2. Calculate Image Distance Rearrange to find \frac{1}{d_i} = \frac{1}{f} - \frac{1}{d_o}. Substitute values: \frac{1}{d_i} = \frac{1}{20} - \frac{1}{30}. 3. Simplify Calculation Calculate \frac{1}{d_i} = \frac{3 - 2}{60} = \frac{1}{60}, so d_i = 60 cm.

Explanation

1. Use Lens Formula<br /> Apply the lens formula $\frac{1}{f} = \frac{1}{d_o} + \frac{1}{d_i}$, where $f = 20$ cm and $d_o = 30$ cm.<br />2. Calculate Image Distance<br /> Rearrange to find $\frac{1}{d_i} = \frac{1}{f} - \frac{1}{d_o}$. Substitute values: $\frac{1}{d_i} = \frac{1}{20} - \frac{1}{30}$.<br />3. Simplify Calculation<br /> Calculate $\frac{1}{d_i} = \frac{3 - 2}{60} = \frac{1}{60}$, so $d_i = 60$ cm.
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