Question

Students in a biology laboratory were asked to view certain cells microscopically and measure the size of a single cell. They were given a compound microscope with an eyepiece of $15$X magnification and an objective lens of $10$X magnification. The eyepiece has a scale with a least count of $10$ $\mu$m. When the students focused the cells under the given microscope, they found that one cell measured $60$ divisions on the eyepiece scale. What is the approximate size of that cell?

• A. $0.47$ $\mu$m
• B. $2.8$ $\mu$m
• C. $4.0$ $\mu$m
• D. $24$ $\mu$m

Answer 1

The correct option is C $4.0$ $\mu$m

The eyepiece has a scale with the count of 10$\mu$m, that is 1 occular division = 10$\mu$m. Under the microscope, one cell measures 60 divisions. Hence, the size of the cell under a microscope will be 60 x 10 = 600 $\mu$m. Compound microscope is having an eyepiece of 15X magnification and an objective lens of 10X magnification. Hence, compound microscope is having magnification of 15 x 10 = 150 times. Hence, the original size of the cell will be 600/150 = 4 $\mu$m.