When observing a specimen under medium power whick adjustment knob should be used to focus on the image Why?

When observing a specimen under medium power, the fine focus adjustment knob should be used to focus on the image. This is because the medium power objective lens has a shorter working distance than lower power lenses, and using the fine focus prevents potential damage to the slide and ensures a clearer image. The coarse focus knob may move the stage too far, risking contact with the slide.