Transcript Title: Magnification

Title: Magnification
Lesson Objectives:
1. Can I calculate magnification, image size
and actual size of a cell? Grade C-A
Starter: Recap quiz….
Recap quiz…
What is the difference between a
micrometer and micrometre?
b. How many micrometres in a millimetre?
c. What is the unit after micrometre?
d. How many micrometres in a nanometre?
e. Calculate the calibration:
X4 objective lens and a x10 eyepiece (=)
Micrometer is 1mm long with 100 divisions
(what is each division worth?)
a.
Magnification
Photomicrographs often have magnification bars to allow
calculation of the actual size of specimens.
4.55μm
The Magic Triangle….
I – Image size
A – Actual size
M – Magnification
Remember: I AM
I
÷
A xM
In this exercise you will calculate the
magnification and/or true size of the
following:
Magnification
1
2
5
6
9
3
4
8
7
10
Before we begin:

Note:

Numbers written like this: 1.26 x 105 mean you
move the decimal point to the right. In this case
you move it 5 times:

1.26 x 105 = 126000.0
1.2 6 0 0 0.0
Before we begin:

Note:

Numbers written like this: 1.26 x 10-5 mean you
move the decimal point to the left. In this case
you move it 5 times:

1.26 x 10-5 = 0.0000126
0.0 0 0 0 1.2 6
Have a go at these:

1.45 x 104 = 14500.0

0.37 x 107 = 3700000.0

86.41 x 10-3 = 0.08641

2.65 x 10-2 = 0.0265
Figure 5.1
x600
Paramecium caudatum
Figure 5.1
Paramecium caudatum
Measured length = 142mm
142 ÷ 600 = 0.237mm
0.237mm = 237μm
x600
Figure 5.2
x9000
chloroplasts
Figure 5.2
chloroplasts
Mean measured length of the four
largest chloroplasts = 39.25mm
39.25 ÷ 9000 = 0.0044mm
0.0044mm = 4.4μm
x9000
Figure 5.3
a bacterium
Measured length = 128mm
128 ÷ 0.002mm = magnification
Magnification = x64000
Figure 5.4
seven week human embryo
Figure 5.4
seven week human embryo
Measure the actual length of the
scale bar and divide by the
length it represents
Magnification = 25 ÷ 10 = x2.5
Figure 5.5
head of a fruit fly
Figure 5.5
head of a fruit fly
Measure the actual length of the
scale bar and divide by the
length it represents
Magnification = 12.5 ÷ 0.2 = x62.5
Figure 5.6
pollen grain
Figure 5.6
pollen grain
(a) Measure the actual length of
the scale bar and divide by
the length it represents
Magnification = 25 ÷ 0.02 = x1250
(b) 47mm
(c) 47 ÷ 1250 = 0.0376mm
0.0376mm = 37.6μm
Figure 5.7
red blood cells in an arteriole
Figure 5.7
red blood cells in an arteriole
Measured length of scale bar = 30mm
Magnification = 30 ÷ 0.01 = x3000
Diameter = 25mm [approx]
Actual diameter = 25 ÷ 3000 = 0.0083mm
0.0083mm = 8.3μm
Figure 5.8
a mitochondrion
Figure 5.8
a mitochondrion
Measured length of scale bar = 30mm
Magnification = 30 ÷ 0.002 = x15000
Measured width = 34mm
Actual width = 34 ÷ 15000 = 0.0023mm
0.0023mm = 2.3μm
Figure 5.9
bacteriophage [a type of virus]
Figure 5.9
bacteriophage [a type of virus]
Measured length of phage = 29mm
Magnification = 29 ÷ 0.0002 = 145000
Magnification = 1.45 x 105
Figure 5.10
potato cells
starch grains
Figure 5.10
potato cells
Mean diameter of the cells = 38mm [approx]
Measured length of scale bar = 24mm
Magnification = 24 ÷ 0.1 = x240
Diameter of the cells = 38 ÷ 240 = 0.158mm
0.158mm = 158μm
Magnification….






The resolving power of the unaided eye is
approximately 0.1mm
The maximum useful magnification of light
microscope is around x1500
Plant and animal cells typically measure
around 20µm
Many organelles are as small as 25nm –
beyond the resolving power of the light
microscope [wavelength of light is 500nm
approx]
Wavelength of electron beam is 0.005nm
Maximum resolving power of the electron
microscope is 0.2nm
Question 11….
Structure
Size
Kind of structure
Visible at
x1500?
bacteriophage
0.2μm
virus
bacterium
2.0μm
prokaryotic cell
 (just)
mitochondrion
2.3μm
eukaryotic organelle

chloroplast
4.4μm
eukaryotic organelle

red blood cell
8.3μm
eukaryotic cell

pollen grain
38μm
eukaryotic cell

potato cell
158μm
eukaryotic cell

paramecium
237μm
eukaryotic organism

embryo
30mm
eukaryotic organism

