2.2 Size of specimens (3)
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1.
The length of a certain cell is measured as 0.15 mm. State this length in micrometres (μm). Show your working.
Answer:
Conversion: 1 mm = 1000 μm
Calculation:
0.15 mm x 1000 μm/mm = 150 μm
Therefore, the length of the cell is 150 μm.
2.
A student is using a microscope to observe a bacterium. The bacterium has a real length of 25 micrometres. The objective lens has a magnification of 40x and the eyepiece lens has a magnification of 10mm. Calculate the total magnification of the microscope and state the apparent length of the bacterium in millimetres.
Total magnification = Eyepiece magnification x Objective magnification
Total magnification = 10mm x 40 = 400x
Size of object in the specimen = (Size observed in the specimen) / (Magnification)
Apparent length of bacterium in the specimen = 25 micrometres / 400 = 0.0625 micrometres
Convert micrometres to millimetres: 0.0625 micrometres x (1mm / 1000 micrometres) = 0.0000625mm
Therefore, the total magnification is 400x and the apparent length of the bacterium is 0.0000625mm.
3.
The actual size of a bacterium is 2 x 10-6 metres. A student observes the bacterium using a microscope with an objective lens of 40x magnification. Calculate the image size observed by the student. Use the formula: magnification = image size ÷ actual size.
Answer:
The formula is: Magnification = Image Size ÷ Actual Size
Rearranging the formula to solve for image size: Image Size = Magnification × Actual Size
Image Size = 40x × (2 x 10-6 m)
Image Size = 8 x 10-5 m
The image size observed by the student is 8 x 10-5 metres.