How do you find the actual size from the magnification and image size?

Actual size = image size ÷ magnification.

How do you find the image size?

Image size = magnification × actual size.

How do you work out total magnification of a light microscope?

Multiply the eyepiece magnification by the objective magnification.

Which objective lens do you start with?

The lowest-power one, with the coarse focus knob.

What is the fine focus knob used for?

Making small adjustments to get a sharp image.

How do you convert 0.05 mm to micrometres?

Multiply by 1000: 0.05 × 1000 = 50 µm.

The ability to show two points close together as separate points.

Give two advantages of an electron microscope over a light microscope.

Greater magnification and greater resolution.

Name four rules for a scientific drawing.

Sharp pencil lines, no shading, ruled labels that do not cross, and a title with the magnification or scale.

Microscopes and measuring cellsIB MYP Biology: Flashcards

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What is the formula for magnification?

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What is the formula for magnification?: Magnification = image size ÷ actual size.
How do you find the actual size from the magnification and image size?: Actual size = image size ÷ magnification.
How do you find the image size?: Image size = magnification × actual size.
How do you work out total magnification of a light microscope?: Multiply the eyepiece magnification by the objective magnification.
Which objective lens do you start with?: The lowest-power one, with the coarse focus knob.
What is the fine focus knob used for?: Making small adjustments to get a sharp image.
How many micrometres are in 1 mm?: 1000 µm.
How many nanometres are in 1 µm?: 1000 nm.
How do you convert 0.05 mm to micrometres?: Multiply by 1000: 0.05 × 1000 = 50 µm.
What is resolution?: The ability to show two points close together as separate points.
Give two advantages of an electron microscope over a light microscope.: Greater magnification and greater resolution.
Name four rules for a scientific drawing.: Sharp pencil lines, no shading, ruled labels that do not cross, and a title with the magnification or scale.

Exam questions on Microscopes and measuring cells

A student prepares a slide of onion skin cells and views it with a light microscope. The eyepiece lens is marked ×10 and the objective lens she selects is marked ×40.
Outline how the student should use the objective lenses and the focus knobs to obtain a clear image.2 marks
A student photographs a human cheek cell through a microscope. The cell in the photograph is 45 mm long. The actual length of the cell is 0.03 mm.
A second diagram of the same cell is drawn at a magnification of ×400. Calculate the length of this diagram in millimetres.2 marks
A student wants to compare the size of onion skin cells with human cheek cells. She prepares a slide of each, views both at the same magnification (×400) and makes a labelled drawing of one cell from each. She then measures the length of each drawing in millimetres.
State a testable hypothesis for the student's investigation, with a scientific reason, and identify the dependent variable.3 marks

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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).