A convex lens produces an inverted image magnified three times of an object placed at a distance of 15 col from it. Calculate focal length of the lens.

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Solution

Here, $u = - 15 c m$

$m = \frac{v}{u} = - 3$ (Since the image is inverted)

$\Rightarrow v = - 3 u = 45 c m$

Now using the lens formula, $\frac{1}{v} - \frac{1}{u} = \frac{1}{f}$

$\Rightarrow \frac{1}{45} - \frac{1}{- 15} = \frac{1}{f}$

$\Rightarrow f = \frac{45}{4} = 11.25 c m$

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A convex lens produces an inverted image magnified three times of an object placed at a distance of 15 col from it. Calculate focal length of the lens.

Here, u=−15 cm m=vu=−3 (Since the image is inverted) ⇒v=−3u=45 cm Now using the lens formula, 1v−1u=1f ⇒145−1−15=1f ⇒f=454=11.25 cm

Here, $u = - 15 c m$

$m = \frac{v}{u} = - 3$ (Since the image is inverted)

$\Rightarrow v = - 3 u = 45 c m$

Now using the lens formula, $\frac{1}{v} - \frac{1}{u} = \frac{1}{f}$

$\Rightarrow \frac{1}{45} - \frac{1}{- 15} = \frac{1}{f}$

$\Rightarrow f = \frac{45}{4} = 11.25 c m$