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Title: Magnification

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Lesson Objectives:

1.Can I calculate magnification, image size and actual size of a cell? Grade C-A

Starter: Recap quiz….

- What is the difference between a micrometer and micrometre?
- How many micrometres in a millimetre?
- What is the unit after micrometre?
- How many micrometres in a nanometre?
- Calculate the calibration:
X4 objective lens and a x10 eyepiece (=)

Micrometer is 1mm long with 100 divisions (what is each division worth?)

Photomicrographs often have magnification bars to allow

calculation of the actual size of specimens.

4.55μm

I – Image size

A – Actual size

M – Magnification

Remember: I AM

I

÷

x

A

M

In this exercise you will calculate the

magnification and/or true size of the

following:

1

2

3

4

5

8

6

7

10

9

- 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

- 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:

1.260000

.

- 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

- 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:

0.00001.2 6

14500.0

- 1.45 x 104 =
- 0.37 x 107 =
- 86.41 x 10-3 =
- 2.65 x 10-2 =

3700000.0

0.08641

0.0265

x600

Figure 5.1 Paramecium caudatum

Measured length = 142mm

142 ÷ 600 = 0.237mm

0.237mm = 237μm

x600

x9000

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

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

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

(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

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

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]

Measured length of phage = 29mm

Magnification = 29 ÷ 0.0002 = 145000

Magnification = 1.45 x 105

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

- 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