magnification

Core and extended

Suppose you were to draw this ant

It’s a huge ant but we are going to say it is 10mm long

The drawing looks about three times the size of the ant

Let us check that more scientifically

We need to measure both the drawing and the ant

Using a ruler measure in millimetres

Measure the longest part but ignore appendages

Length of ant = 10mm

Measure the longest part but ignore appendages

Length of ant = 10mm

Length of drawing = 25mm

Magnification is calculated by:

MagnificationDrawn size

Actual size

= 25mm10mm

Units cancel

Mag X2.5

Length of ant = 10mm

Length of drawing = 25mm

Mag = 25mm10mm

Mag X2.5

Mag X2.5

Ask yourself “does this sound about right?”

In this example we are saying the drawing is magnified X2.5Or it is two and a half times bigger than the actual antAnd that seems about right!

If we draw something smaller than it actually is the magnification should be a fraction

Measure the length but not the shaft

Actual length = 80mm

Measure the length but not the shaft

Drawn length = 40mm

Mag = drawn sizeactual size

= 40mm80mm

Mag X1/2

In other words the drawing was half the size of the actual featherIt was magnified x1/2

Mag X1/2

That sounds about right

We can use a scale bar to find the actual size of an image

First we measure the scale bar

100µm = 20mm100µm = 20 000µm

Next we calculate how much the image has been magnified by seeing how much the scale bar is

magnified

100µm = 20mm100µm = 20 000µmThe scale bar is magnified20 000/100

=X200

What this means is the picture has been magnified 200 times

100µm = 20mm100µm = 20 000µmThe scale bar is magnified20 000/100

=X2000

Next we measure the cell we are interested in

100µm = 20mm100µm = 20 000µmThe scale bar is magnified20 000/100=200times

The cell is 17mmOr 17 000µm

Now we can find the actual length of the cell

100µm = 20mm100µm = 20 000µmThe scale bar is magnified20 000/100=200times

Mag = image size/ actual size

Actual size = image size/mag

= 17000µm/200= 85µm

This cell has a diameter of 85µm

Can you find the magnification of this cell using the scale bar provided?

Remember to convert mm to µm