3. CONVERSION UNITS FOR MICROSCOPES

5. NOW DO THE WORKSHEET ON SIZE AND SCALE

6. LIGHT MICROSCOPES

7. Light microscopes are: Widely used to look at cells Cheap
Can be used anywhere
Can magnify objects upto 2000x or more
School microscopes only magnify upto several 100x
Plant cell magnification 570x

8. ELECTRON MICROSCOPES
These are used to show us in fine detail what is inside a cell
These microscopes can magnify upto 2000,000x
There are two types of electron microscopes:
Transmission electron microscope (give 2D images to very high magnification and resolution)
Scanning electron microscopes (give 3D images but to lower magnification
Electron microscopes are
Large
Expensive
Have to be kept at special temperatures and pressures

11. MITOCHONDRIA
Magnified ~300,000x

12. 800,000x

13. Passion flower pollen seeds
300,000x

15. Atoms of Palladium Metal
X 1000,000

16. CALCULATING MAGNIFICATION
FOR LIGHT MICROSCOPES
MAGNIFICATION OF EYEPIECE LENSE X MAGNIFICATION OF OBJECTIVE LENS
QUESTION
So, if your eyepiece lens is x4 and your objective lens is x10, what is the overall; magnification?

17. CALCULATING THE SIZE OF AN OBJECT

18. ANSWER

19. ANOTHER EXAMPLE
You are looking at onion cells under a microscope. The cells on the slide appear to measure 5 mm with a magnification of x200. What is the actual size of the cell in micrometres (µm)?
ANSWER
NOW DO THE WORKSHEET ON MAGNIFICATION

20. DIFFERENCE BETWEEN MAGNIFICATION AND RESOLVING POWER
Microscopes are really good at magnifying things
If we were magnified by a good light microscope we would look about 3.5km tall
If we were magnified by an electron microscope we would be 3500km tall
The main problem with a light microscope is that it shows limited detail
In other words if we had two separate things but were very close together in a light microscope it would appear as one object
RESOLUTION is the ability to distinguish between two separate points and it is the resolving power of a microscope.
In other words the resolving power of a microscope affects how much detail it can show.

21. A light microscope has a resolving power of about 200nm
A scanning electron microscope has a resolving power of about 10nm
A transmission electron microscope has a resolving power of about 0.2nm
In other words that’s the distance apart of the two atoms in a solid substance.

22. NOW USE THE NEXT POWERPOINT TO LOOK CLOSELY AT THE MECHANICS OF A LIGHT MICROSCOPE