5. After switching from the high-power to the low-powerobjective lens of a compound light microscope, thearea of the low-power field will appearfunction?A)to the right and upB)to the right and downC)to the left and up6. A cell in the field of view of a compound lightmicroscope is shown in the diagram below.In which direction should the slide be moved to centerthis cell in the microscopic field?D)D– holds the specimen on the stage7. A compound light microscope is represented in thediagram below.Which microscope part is correctly paired with itsfunction? Show
When you change from low power to high power on a microscope, the high-power objective lens moves directly over the specimen, and the low-power objective lens rotates away from the specimen. This change alters the magnification of a specimen, the light intensity, area of the field of view, depth of field, working distance and resolution. The image should remain in focus if the lenses are of high quality. Change in MagnificationChanging from low power to high power increases the magnification of a specimen. The amount an image is magnified is equal to the magnification of the ocular lens, or eyepiece, multiplied by the magnification of the objective lens. Usually, the ocular lens has a magnification of 10x. A typical lab-quality standard optical microscope will usually have four objective lenses, running from a low power of 4x to a high power of 100x. With an ocular power of 10x, that gives the standard optical microscope a range of overall magnification from 40x to 1000x. Light Intensity DecreasesThe light intensity decreases as magnification increases. There is a fixed amount of light per area, and when you increase the magnification of an area, you look at a smaller area. So you see less light, and the image appears dimmer. Image brightness is inversely proportional to the magnification squared. Given a fourfold increase in magnification, the image will be 16 times dimmer. Field of ViewGoing to high power on a microscope decreases the area of the field of view. The field of view is inversely proportional to the magnification of the objective lens. For example, if the diameter of your field of view is 1.78 millimeters under 10x magnification, a 40x objective will be one-fourth as wide, or about 0.45 millimeters. The specimen appears larger with a higher magnification because a smaller area of the object is spread out to cover the field of view of your eye. Depth of FieldThe depth of field is a measure of the thickness of a plane of focus. As the magnification increases, the depth of field decreases. At low magnification you might be able to see the entire volume of a paramecium, for example, but when you increase the magnification you may only be able to see one surface of the protozoan. Working DistanceThe working distance is the distance between the specimen and objective lens. The working distance decreases as you increase magnification. The high power objective lens has to be much closer to the specimen than the low-power objective lens in order to focus. Working distance is inversely proportional to magnification. Oil ImmersionMicroscopes magnify an object's appearance by bending light. Higher magnification means the light is bent more. At a certain point, the light is bent so much that it can't make it through the objective lens. At that point – usually around 100x for standard lab microscopes – you'll need to put a drop of oil between your specimen and the objective lens. The oil "unbends" the light to stretch out the working distance and make it possible to image at high magnifications. Microscope NotesThe compound microscope is a useful tool for magnifying objects up to as much as 1000 times their normal size. Using the microscope takes lots of practice. Follow the procedures below both to get the best results and to avoid damaging the equipment.
Field of ViewThe field of view is largest on the lowest power objective. When you switch to a higher power, the field of view closes in towards the center. You will see more of an object on low power. Therefore, it is best to find an object on low power, center it, and then switch to the next higher power and repeat. Depth of FocusThe depth of focus is greatest on the lowest power objective. Each time you switch to a higher power, the depth of focus is reduced. Therefore a smaller part of the specimen is in focus at higher power. Again, this makes it easier to find an object on low power, and then switch to higher power after it is in focus. A common exercise to demonstrate depth of focus involves laying three different colored threads one on top of the other. As the observer focuses down, first the top thread comes into focus, then the middle one, and finally the bottom one. On higer power objectives one may go out of focus as another comes into focus. Microscope TroubleshootingProblem #1: The image is upside down and/or backwards.
Problem #2: Everything is dark.
Problem #3: I can't find anything on low power!
Problem #4: When I moved to a higher power, everything disappeared!
Problem #5: The image is blurry on all powers.
Problem #6: The image is blurry only on a particular power.
Microscope DrawingsWhen drawing what you see under the microscope, follow the format shown below. It is important to include a figure label and a subject title above the image. The species name (and common name if there is one) and the magnification at which you were viewing the object should be written below the image. All relevant parts of the drawing should be labelled on the right side of the image using straight lines. Lines should not cross. Drawings should be done in pencil, while labels should be in pen or typed. Remember that total magnification is determined by multiplying the ocular x objective. Viewing Prepared Slides*** Don't hoard slides! You can only view one at a time, so that's all you should be holding. Return it before getting another, and if you break it, tell your instructor so that it can be properly cleaned up and replaced! ***
Making a Wet Mount (Live Prep) Slide
Further InvestigationDigital microscope for Macintosh or Windows Investigating pondwater organisms Powers of 10 (1977 version) Make your own microscope What happens when you switch from high to low power on a microscope?When you switch to a higher power, the field of view is closes in. You will see more of an object on low power. The depth of focus is greatest on the lowest power objective. Each time you switch to a higher power, the depth of focus is reduced.
When the microscope is changed from low power to high power the distance between the objective lens and the cover slip of the slide will?When you switch from low-power objective lens to a higher-power objective lens, what happens to the working distance between the lens and the coverslip? It decreases. When you change from a low-power objective lens to a higher one, what happens to the field of view? It increases.
What is the magnification of the low power objective on a compound light microscope?Low Power Objective (10x)
The total magnification of a low power objective lens combined with a 10x eyepiece lens is 100x magnification, giving you a closer view of the slide than a scanning objective lens without getting too close for general viewing purposes.
How did the light intensity change when you switched from low power to high power objective?What change occurred in the light intensity of the field of view when you exchanged the low-power objective for the high-power objective? Light intensity is decreased when high-power objective is used.
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