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24/09/2021 9:03 pm
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A concave lens of focal length 15 cm forms an image 10 cm from the lens. How far is the object placed from the lens. Draw the ray diagram.
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24/09/2021 9:08 pm
The complete ray diagram is shown below:
Given: f = -15 cm, v = -10 cm, u = ?
Applying the formula \(\frac{1}{f}\) = \(\frac{1}{v}\) - \(\frac{1}{u}\), we get
\(\frac{1}{u}\) = \(\frac{1}{v}\) - \(\frac{1}{f}\)
= \(\frac{1}{-10}\) + \(\frac{1}{15}\)
= \(\frac{-3+2}{30}\) = \(\frac{-1}{30}\)
⇒ u = -30 cm
Hence, the object is placed at a distance of 30 cm from the lens.