A student wants to view cells under the compound microscope at a total magnification of 400X. If the eyepiece is 10X, which objective lens should be used?

To achieve a total magnification of 400X with a compound microscope that has a 10X eyepiece, you need to select an objective lens that will work in conjunction with the eyepiece to produce the desired magnification. The total magnification of a microscope is calculated by multiplying the magnification power of the eyepiece by the magnification power of the objective lens.

In this case, since the eyepiece magnification is 10X, you can determine the required objective lens magnification by dividing the desired total magnification (400X) by the eyepiece magnification (10X):

400X (total magnification) ÷ 10X (eyepiece magnification) = 40X (objective lens magnification).

Thus, the objective lens with a magnification of 40X is the correct choice, as it allows for a total magnification of 400X when paired with the 10X eyepiece. This reasoning ensures that the student can successfully view the cells at the appropriate scale for analysis.