MicroscopesMicroscopesSC.912.L.14.4 Compare and contrast structure and function of various types of microscopes.

Essential QuestionEssential Question

How do different types of How do different types of microscopes work?microscopes work?

Use of MicroscopeUse of Microscope

To magnify objects that cannot be seen To magnify objects that cannot be seen with the naked eyewith the naked eye

Resolving power Resolving power Ability of microscope to distinguish objects as Ability of microscope to distinguish objects as

separate – measured in nm and the lower the separate – measured in nm and the lower the number the smaller the object that can be number the smaller the object that can be distinguisheddistinguished

Comparing Powers of Magnification

We can see better details with higher the powers of magnification, but we cannot see as much of the image.

Which of these images would be viewed at a

higher power of magnification?

Types of MicroscopesTypes of Microscopes

Dissecting microscopeDissecting microscope 3D images3D images Relies on light on top of Relies on light on top of

imageimage Low magnificationLow magnification

Compound light microscopeCompound light microscope Observe living thingsObserve living things Magnifies up to 2000 timesMagnifies up to 2000 times Resolving power – 500 nmResolving power – 500 nm

Compound Light Microscope

Types of MicroscopesTypes of Microscopes Electron MicroscopesElectron Microscopes

Transmission electron microscope (TEM)Transmission electron microscope (TEM)• 2-D image Magnify hundreds of thousands of times2-D image Magnify hundreds of thousands of times

• Resolution as great as 0.2 nmResolution as great as 0.2 nm Scanning electron microscope (SEM)Scanning electron microscope (SEM)

• 3D image3D image

• Lower magnification than TEMLower magnification than TEM

Sample must be frozen or embedded on Sample must be frozen or embedded on plastic – not livingplastic – not living

Electron beam wavelengths are shorter Electron beam wavelengths are shorter than light wavelengths, so better resolving than light wavelengths, so better resolving power.power.

Transmission Electron Microscope (TEM) Scanning Electron Microscope (SEM)

Light Microscope Transmission Electron Microscope

Scanning Electron Microscope

Radiation Source light electrons Electrons

Wavelength 400 – 700 nm 0.005 nm 0.005 nm

Lenses glass electromagnetic Electromagnetic

Specimen living or non livingsupported on glass slide

non-living supported on a small copper grid in a vacuum

non-living supported on a metal disc in a vacuum

Maximum Resolution

200 nm 1 nm 10 nm

Maximum Magnification

1500 X 250 000 X 100 000 X

Stains colored dyes impregnated with heavy metals

coated with carbon or gold

Type of Image colored monochrome (black & white)

monochrome (black & white)

TYPES OF MICROSCOPESDirections: Copy this table onto your composition book.

How do you work out the How do you work out the magnification of your magnification of your

microscope?microscope?

Ocular magnification X Objective magnificationOcular magnification X Objective magnification

Essential Question

A Lens

• Enlarges an image and bends the light toward your eye.

Eyepiece (Ocular) Lens

Usually has a power of 10 x

How to Calculate Total Magnification

Eyepiece (Ocular) Lens

X

Objective Lens

=

Total Magnification

What’s my power?

To calculate the power of magnification, multiply the power of the ocular lens by the power of the objective.

What are the powers of magnification for each of the objectives we have on

our microscopes?

Rotary nosepiece of your microscope has objective lenses attached.

You will always be looking through the ocular and objective lens simultaneously, so multiply ocular magnification x objective power to calculate the Total Magnification (xTM).

Shortest lens (red band) should have been pointing down when your scopes were last put away.

The Objective Lenses

Image: Microscope objective lenses, T. PortFrom the Virtual Microbiology Classroom on ScienceProfOnline.com

Scanning Power

Image: Microscope objective lenses, T. Port

• Red band around it.

• Magnifies objects 4x.

• Q: What is the Total Magnification? ____ TM

From the Virtual Microbiology Classroom on ScienceProfOnline.com

Low Power

• Has yellow band around it.

• Magnifies objects 10x.

• Q: What is the Total Magnification? ____ TM

Image: Microscope objective lenses, T. PortFrom the Virtual Microbiology Classroom on ScienceProfOnline.com

High Dry

• Has blue band around it.

• Magnifies objects 40x.

• Q: What is the Total Magnification? ____ TM

Image: Microscope objective lenses, T. PortFrom the Virtual Microbiology Classroom on ScienceProfOnline.com

Let’s give it a try ...1 – Turn on the microscope and then rotate the nosepiece to click the red-banded objective into place.

2 – Place a slide on the stage and secure it using the stage clips. Use the coarse adjustment knob (large knob) to get it the image into view and then use the fine adjustment knob (small knob) to make it clearer.

4 – When you are done, turn off the microscope and put up the slides you used.

3 – Once you have the image in view, rotate the nosepiece to view it under different powers. Draw what you see on your composition book/

Be careful with the largest objective! Sometimes there is not enough room and you will not be able to use it!

Microscope TechniquesMicroscope Techniques

Making a wet slideMaking a wet slide Add a drop of water to Add a drop of water to

center of slidecenter of slide Place object in water (do Place object in water (do

not let it get folded)not let it get folded) Use Use forcepsforceps to position to position

coverslip (fingerprints will coverslip (fingerprints will interfere)interfere)

Lower coverslip slowly to Lower coverslip slowly to avoid air bubblesavoid air bubbles

• Always carry with 2 hands

• Only use lens paper for cleaning

• Do not force knobs

• Always store covered

• Keep objects clear of desk and cords

PRACTICE QUESTIONS

1. What is the difference between a light microscope and an electron microscope?

2. If the ocular lens is 8x magnification and the objective lens is 20x, what is the total magnification?

3. Why should the coarse adjustment knob not be used with the high power objective lens?

4. Describe how to correctly prepare the microscope for storage.