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

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

Use of Microscope To magnify objects that cannot be seen with the naked eye Resolving power Ability of microscope to distinguish objects as separate – measured in nm and the lower the number the smaller the object that can be distinguished

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 Microscopes Dissecting microscope 3D images Relies on light on top of image Low magnification Compound light microscope Observe living things Magnifies up to 2000 times Resolving power – 500 nm Compound Light Microscope

Types of Microscopes Electron Microscopes Transmission electron microscope (TEM) 2-D image Magnify hundreds of thousands of times Resolution as great as 0.2 nm Scanning electron microscope (SEM) 3D image Lower magnification than TEM Sample must be frozen or embedded on plastic – not living Electron beam wavelengths are shorter than light wavelengths, so better resolving power.

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

TYPES OF MICROSCOPES Directions: Copy this table onto your composition book. Light Microscope Transmission Electron Microscope Scanning Electron Microscope Radiation Source light electrons Electrons Wavelength 400 – 700 nm 0.005 nm Lenses glass electromagnetic Electromagnetic Specimen living or non living supported 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)

How do you work out the magnification of your microscope? Essential Question How do you work out the magnification of your microscope? Ocular magnification X Objective magnification

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?

The Objective Lenses 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. From the Virtual Microbiology Classroom on ScienceProfOnline.com Image: Microscope objective lenses, T. Port

Scanning Power Red band around it. Magnifies objects 4x. Q: What is the Total Magnification? ____ TM From the Virtual Microbiology Classroom on ScienceProfOnline.com Image: Microscope objective lenses, T. Port

Has yellow band around it. Low Power Has yellow band around it. Magnifies objects 10x. Q: What is the Total Magnification? ____ TM From the Virtual Microbiology Classroom on ScienceProfOnline.com Image: Microscope objective lenses, T. Port

Q: What is the Total Magnification? ____ TM High Dry Has blue band around it. Magnifies objects 40x. Q: What is the Total Magnification? ____ TM From the Virtual Microbiology Classroom on ScienceProfOnline.com Image: Microscope objective lenses, T. Port

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

Microscope Techniques Making a wet slide Add a drop of water to center of slide Place object in water (do not let it get folded) Use forceps to position coverslip (fingerprints will interfere) Lower coverslip slowly to avoid air bubbles

Microscope Care 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 Teacher demonstrates how to hold the microscope, where the lens paper is located and how to use it. Students will be invited to turn the knobs and observe the stage as it moves up and down. Teacher will demonstrate how to store the microscope.

PRACTICE QUESTIONS What is the difference between a light microscope and an electron microscope? If the ocular lens is 8x magnification and the objective lens is 20x, what is the total magnification? Why should the coarse adjustment knob not be used with the high power objective lens? Describe how to correctly prepare the microscope for storage.