Question

What type of objective lens will have the least working distance?
A. 5X
B. 10X
C. 45X
D. 100X

Answer 1

Hint:-
 A microscope is an instrument that is used to see minute objects that our naked eyes can't see and the science which deals with studying small objects using microscopes is called Microscopy. The parts of the microscope involve a single eyepiece, eyepiece tube, three objective lenses, adjusting knob, Condenser, Iris, Diaphragm.

Complete step-by-step solution:-In a microscope, the optical element which lies closest to the specimen is the objective lens. It gathers light from the specimen which produces a real image that is seen via an ocular lens or eyepiece. Objective lenses have a multi-element design which makes them the most important and most complex part of the microscope.
Objective lenses are responsible for the primary image, its total magnification, and the quality and resolution of the image. Based on the magnification power, the objective lens is of the following types:
Low magnification objective lens (5X and 10X)
Intermediate magnification objective lens (20X and 40X)
High magnification objective lens (100X)
Working distance is the distance between the specimen and the first lens where light waves are reflected. So the high magnification objective lens has to be closer to the specimen to focus the object and the low magnification objective lens requires more distance to focus the object. So, the working distance will decrease with an increase in magnification.
As working distance is inversely proportional to the magnification, the more the magnification the least will be the working distance. So, the objective lens with 100X Magnification will have the least working distance and an objective lens with magnification 5X will have maximum working distance. So, the correct answer is an option (D) 100X.

Note:-
 Microscope has two lenses, an Ocular lens with magnification 10X and an Objective lens with magnification 4X, 40X, 100X. The total magnification produced by the combination of the Ocular lens and Objective lens is different from their magnification and is calculated by multiplying the magnification of the Ocular lens with a magnification of the Objective lens.