Question

question
why should the fine focus knob typically be used with the 10x and 40x objective lenses?
the slide should be close to in focus after focusing at the 4x objective. focusing with the coarse focus knob would result in too large a change in focus.
focusing using the coarse adjustment knob with the 10x or 40x objective may crack the stage.
the coarse focus knob is nonfunctional with the 10x and 40x objective lenses.

Explanation:

• For the first option: When using a microscope, we first focus with the 4X (low - power) objective. After that, when we switch to 10X or 40X (higher - power) objectives, the slide is already nearly in focus. The coarse focus knob makes large - scale changes in focus. Using it at higher magnifications can cause the objective lens to crash into the slide or make the focus change too much to get a clear image. So we use the fine focus knob which makes small, precise adjustments.
• For the second option: Using the coarse focus knob with 10X or 40X objectives does not typically crack the stage. The main issue is the focus adjustment, not damage to the stage.
• For the third option: The coarse focus knob is functional with 10X and 40X objective lenses, but it's not recommended because of the large focus change it causes.

Answer:

A. The slide should be close to in focus after focusing at the 4X objective. Focusing with the coarse focus knob would result in too large a change in focus.