Question

To increase the angular magnification of a simple microscope, one should increase
A) the focal length of the lens
B) the power of the lens
C) the aperture of the lens
D) the object size

Answer 1

This question is based on the microscope. We know that a microscope is an optical instrument that uses a lens to allow magnified images of distant objects, mainly the objects which cannot be seen by the unaided eye. And we use the formula of angular magnification to get the answer of this question.

Complete step by step answer:
First, we have to know the term angular magnification. The angular magnification is equal to the fraction of the tangents of the angles subtended by an object and its image to that of the subtended at the eye by the object when not viewed through the instrument.
Now, write the expression for the angular magnification for normal adjustment is given as,
$m = \dfrac{D}{f}$
Here, $D$ is the least distance of distant vision and f is the focal length.
The expression for the angular magnification for near point is given as,
$m = \left( {1 + \dfrac{D}{f}} \right)$
In normal adjustment the object is positioned at a distance equal to focal length from the lens of the simple microscope.
Near the point, the object is placed on the focal length. So, the lens power is inversely proportional to focal length.
Hence, if we have to increase the angular magnification of the microscope, the optical power of the lens should be increased.

So, the correct answer is “Option B”.

Note:
In this question, students must have knowledge of angular magnification, simple microscope and power of lens. The object is positioned on the focal length of the lens to find the relation between angular magnification and power.