Answer key: Microscope Magnification Activity

For teachers. This page is hidden from search engines and not linked from student pages, but it is not password-protected, so please don’t share the link with students. Student activity: Microscope Magnification Activity.

Goal: Calculate magnification, actual size and image size with M = image size ÷ actual size, convert between millimeters and micrometers, and work out total microscope magnification.

Connects to NGSS MS-LS1-1 (Conduct an investigation to provide evidence that living things are made of cells.)

Completed results table

Every value is the tool’s own readout for that setting, calculated with the same code as the Magnification & scale bar calculator.

Answers

1. A drawing of a cell is 20 mm wide at 400× magnification. Show how to find the cell’s actual size in micrometers.

   Convert first: 20 mm × 1,000 = 20,000 µm. Actual size = image size ÷ magnification = 20,000 ÷ 400 = 50 µm.

2. A red blood cell 7.5 µm across is drawn 7.5 mm wide. A student says the magnification is 1×. What mistake did they make, and what is the right answer?

   They divided without converting to the same unit. 7.5 mm = 7,500 µm, so M = 7,500 ÷ 7.5 = 1,000×.

3. How large does a 2 µm bacterium appear at 1,000×?

   Image size = actual size × magnification = 2 µm × 1,000 = 2,000 µm, which is 2 mm.

4. What is the total magnification with a 10× eyepiece and a 40× objective? How many 50 µm cells fit across the 450 µm field of view?

   Total magnification = 10 × 40 = 400×. 450 ÷ 50 = 9 cells fit across the field.

5. When you switch from the 4× objective to the 40× objective, the magnification rises 10 times. What happens to the field of view?

   It shrinks 10 times, from 4,500 µm (4.5 mm) to 450 µm, so you see a smaller area in more detail.

6. Challenge: a scale bar on a micrograph is labeled 20 µm and measures 8 mm on the page. What is the magnification?

   8 mm = 8,000 µm, so M = 8,000 ÷ 20 = 400×.