Everything Life Sciences Grade 10

If magnification is increased 10-fold, the field of view will decrease 10 fold. Thus it will

become 0.1 mm. What this means is that at higher magnification, we are able to see objects

of smaller and smaller size within our field of view. This is why at higher magnification, the

field of view becomes smaller.

At 500X magnification, the field of view of a microscope is 0,05 mm. What will the field of

view be at 100X magnification?

x=

500

100

×0,05 mm

=0,25 mm

Calculating magnification and using scale bars

When drawing cells or cellular structures, your diagrams will usually be much larger than

the actual size of the structures you will be drawing. The magnification is given by:

magnification=

drawing size

actual size

When a scale bar is provided with the diagram, the magnification is given by:

magnification=drawing size×

scale given

measured length of scale

Worked example 1: Calculating overall magnification

QUESTION

Calculate the overall magnification of a compound light microscope with a magnification of

10 X due to the eyepiece and a magnification of a 100X due to the objective lens.

SOLUTION

Using the formula:

overall magnification=power of eyepiece×power of objective

= 10× 100

= 1000×the original size

Worked example 2: Calculating size of object from its microscopic image

QUESTION

If the measured length of the magnified beetle larva image shown below was 2 centimetres

(20 mm), the ocular magnification of the microscope is 5X and you are using an objective

lens magnification of 10X, what is the actual length of the larva in millimetres?

68 3.2. Molecular make up of cells