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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.