CONVERSION UNITS FOR MICROSCOPES

NOW DO THE WORKSHEET ON SIZE AND SCALE

LIGHT MICROSCOPES

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

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

MITOCHONDRIA Magnified ~300,000x

800,000x

Passion flower pollen seeds 300,000x

Atoms of Palladium Metal X 1000,000

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?

CALCULATING THE SIZE OF AN OBJECT

ANSWER

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

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.

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.

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