Question

# The least distance of distinct vision is $25cm$ . The focal length of a convex lens of a simple microscope is $5cm$ . Its magnifying power if the image is at a near point a. $4$b. $5$c. $6$d. $7$

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Hint: Good optical device is that which is requiring a clear image with proper resolution. The magnification parameter plays an important role in it. We refer to magnification as the ratio of the size of the image to the size of the object.

Given: The least distance of distinct vision $D = 25cm$ .
The focal length of the simple microscope $f = 5cm$ .
So we are aware that for a simple microscope, the magnification $m$ is given by the formula:
$m = 1 + \dfrac{D}{f}$
Here $m$ is the magnification, $D$ is the least distance of distinct vision, and $f$ is the focal length.
Now, we can substitute $D = 25cm$, $f = 5cm$ to find the value of magnification $m$ .
$\therefore m = 1 + \dfrac{{25}}{5}$
On further solving we get,
$m = 1 + 5$
$\Rightarrow m = 6$

Hence, the correct answer is option (C).