Where is the position of the image when an object is placed at a distance of 10 cm from a convex lens of focal length 10 cm?

A
At focus
B
At infinity
C
Behind the lens
D
Beyond $2 f$

Solution:

The position of the image is at infinity when an object is placed at a distance of $10 cm$ from a convex lens of focal length $10 cm$ .
Given that,
Distance $u = - 10 cm$ (negative sign indicates behind the lens)
Focal length $f = + 10 cm$ (positive: as the lens is convex)
Now, by the lens formula,
$\frac{1}{f} = \frac{1}{v} - \frac{1}{u}$
$\Rightarrow \frac{1}{10} = \frac{1}{v} - \frac{1}{- 10}$
$\Rightarrow \frac{1}{v} = \frac{1}{10} + \frac{1}{- 10}$
$\Rightarrow \frac{1}{v} = 0$
$\Rightarrow v = \infty$
Hence, the image is formed at infinity.

Where is the position of the image when an object is placed at a distance of $10 cm$ from a convex lens of focal length $10 cm$ ?

Solution:

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