Microscope Master

Microscope Master

Cells are far too small to see with the naked eye, so we magnify them. But magnifying is only half the story, and the maths behind it wins (or loses) real marks. By the end you'll pick the right microscope, explain resolving power, and calculate magnification. Units and all.

Two kinds of microscope

Two things matter, and they are not the same. **Magnification** is how many times bigger the image is. **Resolving power** is the ability to tell two very close points apart, and it is what decides how much DETAIL you see. Magnify beyond your resolving power and all you get is a bigger blur:

Which microscope?

A scientist needs to see the detailed internal structure of a ribosome. Which microscope should they use, and why?

• Electron. It has much higher resolving power
• Light. It can view living samples
• Either. They show the same detail
• Neither can show a ribosome

Mark the claims

A student has written five statements about microscopes. Tap the TWO that are WRONG.

• An electron microscope has both higher magnification and higher resolving power than a light microscope.
• An electron microscope can be used to watch a living cell divide.
• Resolving power is the ability to tell two very close points apart.
• Magnifying an image more will always reveal more detail.
• A light microscope is cheaper and more portable than an electron microscope.

The magnification triangle

One formula ties it together: **image size = magnification × real size**. Put image size on top of the triangle with magnification and real size below, and cover the one you want:

Work out the magnification

A cell has a real width of 0.05 mm. Under the microscope, its image is 10 mm wide. What is the magnification? (magnification = image ÷ real size)

Units and standard form

Cells are measured in tiny units, so convert before you calculate: - **1 mm = 1000 µm** (micrometres) - **1 µm = 1000 nm** (nanometres) Very small sizes are often written in **standard form**: 0.002 mm = 2 × 10⁻³ mm = 2 µm. The classic dropped mark is doing the division correctly and then forgetting the **mm → µm** step, or leaving the answer in mm when the question asked for µm. Read the unit the question wants BEFORE you start, and underline it.

Now with a conversion

A structure's image is 6 mm wide at a magnification of ×3000. What is its real width in micrometres (µm)? (real size = image ÷ magnification, then convert mm → µm)

Predict the image

A mitochondrion is 2 µm long. You draw it at a magnification of ×5000. How long is your drawing in millimetres (mm)? (image size = magnification × real size, then convert µm → mm)

The method, in order

Put the steps of a magnification calculation into the order you should do them.

• Read the question and note which unit the answer has to be in
• Write down the image size and the real size
• Convert one of them so that both are in the same unit
• Divide the image size by the real size
• Write the answer with a × in front of it and no unit after it

Take the picture

You have been asked to find out whether the mitochondria in a sample of muscle cells have changed shape. Work through the job.

• A light microscope cannot resolve a mitochondrion clearly. What do you use, and why?
• What does that mean for your sample?
• A mitochondrion measures 2 µm and your image of it is 8 mm across. Before you divide, what must you do?

In the exam

An electron microscope has higher _____ power than a light microscope, which is why it shows finer detail, but only a light microscope can view _____ cells. To find magnification, divide the image size by the _____ size, having first converted both to the same unit. Magnification itself has no _____, so it is written as a number with a × in front.