The fine adjustment knob on the microscope
A.
Locates the specimen.
B.
All of the answer choices are correct.
C.
Locates the focus plane.
D.
Fine-tunes the focus.
The Correct answer and Explanation is:
The correct answer is D. Fine-tunes the focus.
The fine adjustment knob on a microscope plays a critical role in achieving precise focus on a specimen, especially when viewing it under higher magnifications. The microscope typically has two focus knobs: the coarse adjustment knob and the fine adjustment knob. The coarse adjustment knob is used for large-scale focusing, allowing the user to quickly bring the specimen into a rough focus. This knob moves the stage (or the objective lens) up and down more significantly, making substantial changes in the focus plane.
In contrast, the fine adjustment knob makes very small, precise adjustments to the focus. This is particularly important when working at higher magnifications, such as 40x or 100x, where the depth of field is very shallow. At these magnifications, even slight movements can blur the image, so the fine adjustment knob is necessary to bring the specimen into sharp focus without overshooting.
This fine-tuning capability allows users to see details that would otherwise be missed with only coarse adjustment. For instance, when examining cellular structures, the fine adjustment knob helps in resolving the intricate details within the cells, such as the nucleus, organelles, or even smaller components like mitochondria.
The other options in the question do not accurately describe the function of the fine adjustment knob. Option A, “Locates the specimen,” refers to positioning the slide, which is usually done manually or with the mechanical stage controls. Option C, “Locates the focus plane,” is more relevant to the coarse adjustment knob’s function. Therefore, the primary function of the fine adjustment knob is to fine-tune the focus, making it an indispensable tool for obtaining a clear and detailed image of the specimen under observation.