A-Level Biology (AQA) – Magnification calculations & resolution

3.6 - Magnification Calculations & Resolution

1The definitions of magnification and resolution
2How to calculate magnification

9 min

Magnification

Magnification is how many times larger an image is than the object.

For example, here the image is 1,000 larger than the object, so its magnification is x 1,000.

Diagram showing an image magnified 1,000 times larger than the object.

Resolution

Resolution is the ability to distinguish between two separate points (or how detailed the image is).

For example, both images here have the same magnification, but the left image has a higher resolution.

Comparison of two microscope images showing the difference between high and low resolution.

Calculating magnification

To calculate magnification, you need to know the image size and the object size:

Image size - How large the object appears when you view it through a microscope.
Object size (actual size) - The real size of the object.

The equation for calculating magnification is:

$magnification = \frac{image size}{object size}$

When calculating magnification, all lengths must be in the same unit. This may require converting from one unit to another.

Diagram showing unit conversions from centimetres to millimetres to micrometres to nanometres.

Worked example - Calculating magnification

A plant cell in a micrograph measures 40 mm in width. If the real width of the plant cell is actually 20 µm, what is the magnification?

Step 1: Equation

$magnification = \frac{image size}{object size}$

Step 2: Conversion

to convert from mm into μm, multiply by 1,000

$image size = 40 \times 1,000 = 40,000$ μm

$object size = 20$ μm

Note: the units for image size and object size need to be the same before they are put into the magnification calculation

Step 3: Substitution and correct evaluation

$magnification = \frac{40,000}{20}$

$magnification = x 2,000$

Worked example - Calculating image size

A sperm cell is 5 µm long. How long will it appear in mm when viewed under a microscope with a magnifying power of x 1,500?

Step 1: Equation

$magnification = \frac{image size}{object size}$

Step 2: Rearrangement

$image size = magnification \times object size$

Note: we need to rearrange the equation to make image size the subject

Step 3: Substitution and correct evaluation

$image size = 1,500 \times 5$

$image size = 7,500$ µm

Step 4: Conversion

to convert µm into mm, divide by 1,000

$image size = \frac{7,500}{1,000}$

$image size = 7.5$ mm

3.6 - Magnification Calculations & Resolution

1The definitions of magnification and resolution
2How to calculate magnification

9 min

Magnification

Magnification is how many times larger an image is than the object.

For example, here the image is 1,000 larger than the object, so its magnification is x 1,000.

Resolution

Resolution is the ability to distinguish between two separate points (or how detailed the image is).

For example, both images here have the same magnification, but the left image has a higher resolution.

Calculating magnification

To calculate magnification, you need to know the image size and the object size:

Image size - How large the object appears when you view it through a microscope.
Object size (actual size) - The real size of the object.

The equation for calculating magnification is:

$magnification = \frac{image size}{object size}$

When calculating magnification, all lengths must be in the same unit. This may require converting from one unit to another.

Worked example - Calculating magnification

A plant cell in a micrograph measures 40 mm in width. If the real width of the plant cell is actually 20 µm, what is the magnification?

Step 1: Equation

$magnification = \frac{image size}{object size}$

Step 2: Conversion

to convert from mm into μm, multiply by 1,000

$image size = 40 \times 1,000 = 40,000$ μm

$object size = 20$ μm

Note: the units for image size and object size need to be the same before they are put into the magnification calculation

Step 3: Substitution and correct evaluation

$magnification = \frac{40,000}{20}$

$magnification = x 2,000$

Worked example - Calculating image size

A sperm cell is 5 µm long. How long will it appear in mm when viewed under a microscope with a magnifying power of x 1,500?

Step 1: Equation

$magnification = \frac{image size}{object size}$

Step 2: Rearrangement

$image size = magnification \times object size$

Note: we need to rearrange the equation to make image size the subject

Step 3: Substitution and correct evaluation

$image size = 1,500 \times 5$

$image size = 7,500$ µm

Step 4: Conversion

to convert µm into mm, divide by 1,000

$image size = \frac{7,500}{1,000}$

$image size = 7.5$ mm