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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? How many micrometres in a millimetre?

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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
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?)

magnification
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

The Magic Triangle….

I

÷

x

A

M

magnification1
Magnification

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

before we begin
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

1.260000

.

before we begin1
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

0.00001.2 6

have a go at these
Have a go at these:

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

slide10
Figure 5.1 Paramecium caudatum

Measured length = 142mm

142 ÷ 600 = 0.237mm

0.237mm = 237μm

x600

slide12
Figure 5.2 chloroplasts

Mean measured length of the four largest chloroplasts = 39.25mm

39.25 ÷ 9000 = 0.0044mm

0.0044mm = 4.4μm

x9000

slide13
Figure 5.3 a bacterium

Measured length = 128mm

128 ÷ 0.002mm = magnification

Magnification = x64000

slide15
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

slide17
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

slide19
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

slide21
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

slide23
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

slide25
Figure 5.9 bacteriophage [a type of virus]

Measured length of phage = 29mm

Magnification = 29 ÷ 0.0002 = 145000

Magnification = 1.45 x 105

slide27
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

magnification2
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
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