Microscopes 4th Grade NMGK-12 Project 102 This slide presentation is designed to enhance a lesson on microscope use and observation of animal and plant cells.

40 to 1000 times larger than life Microscopes are used to see objects or parts of objects that are too small to be seen clearly by the naked human eye. Compound microscopes are designed to magnify objects 40 to 1000 times larger than life. Magnification in a microscope can be calculated by multiplying the magnification of the objective lens being used by the magnification of the ocular lens (this is usually 10x, sometimes 15 or 20x).

view fine detail on small objects Hair One purpose of magnifying something is to see fine detail on objects. For example, if you look at a piece of human hair with your eye, it looks like a smooth string, but if you look at it under high enough magnification (this example is >1000x) you can see the detail the growth of the hair by addition at the base (fine “squiggles” on the hair). Another good example is to put a flea under magnification to see legs and the hairs on the legs. A good non-biological example is to put a piece of colored (or black and white) newsprint picture under the scope and show the students the dots that make up the picture. With the eye our resolution is too small to make out all of the individual spots, but the magnification by the microscope increases resolution so that they can be seen.

light shined through the object from underneath Different microscopes allow different types of specimens to be observed, depending on the light, or energy source. Compound microscopes use transmitted light. That is light that is transmitted through the object to the eye. To see more detail on tiny specimens (or to see prokaryotic cells), an oil immersion lens can be used on the compound microscope. This lens is designed to be placed into a layer of oil (on the specimen or coverslip) and create an uninterrupted liquid layer between the specimen and the objective. By removing the layer of air that is between normal objectives and the specimen, more light is retained and higher magnification is possible. Dissecting microscopes use reflected light. This light is shined from above the object and reflected back to the eye. Compound microscopes can only be used to magnify small, thin objects that light can shine through. Dissecting microscopes are used to see larger objects in which light can not pass through. Electron microscopes are used to increase magnification much higher than compound scopes are able and use electrons bounced off from the specimen. These electrons are captured by sensors in the microscope which can interpret and picture the surface structure of the specimen.

Parts of the Compound Microscope eyepiece objectives coarse focus knob stage Eyepiece - ocular lens, magnifying lens that you look through (10x usually) Objectives - magnifying lenses that collect light from around the specimen and pass it to the eyepieces, usually 2-4 on each microscope with magnifications of 4-100x Stage - flat platform, with hole to allow light through, that the slide/specimen is placed on Focus Knobs - move the stage up and down so that the specimen can be put into the most clear view through the two lenses. Usually fine and coarse focus knobs. Coarse should be used at low magnification and fine at higher magnifications. (Care should be taken not to “crush” the slide while focusing). Light - source of light for viewing the specimen, some microscopes may have mirrors which are useful for outside use but electric lights are more reliable in the lab. Base - heavy portion of the microscope that sits on the work table and holds the rest of the microscope fine focus knob light base

Using the Microscope do not move the microscopes use only the fine focus knobs on the compound microscopes focus SLOWLY use both eyes (do not close one) Set up the microscopes so that the students do not have to move them too much. The more movement or jarring, the more likely damage to the microscope. Using the coarse focus knob at higher magnification increases the likelihood of crushing slides because the specimen is so close to the objective. Most microscopes are confocal, which means that once focusing is done at lower magnifications, very little, if any, focusing should need to be done as objectives are exchanged (if the slide is not moved or disrupted) Focus slowly, do not crank the focus knobs as it increases the chances of crushing the slide If you have binocular microscopes, use both eyes to view the specimen. Squinting and using only one eye causes eye strain and makes it more difficult to see. Most binocular microscopes have adjustable ocular lenses that can be moved closer together or farther apart or one focused separate from the second to allow for unequal eyes. One a monocular microscope, it may be easier on the eye to keep both open while you look through the microscope with the other. This may take practice though.