Microscope
The microscope, which consists of two converging lenses, was invented by Zacharius Janssen about 1590.
In the microscope the lower lens is called the objective lens and the object to be viewed is placed just outside its focus, to form a magnified inverted real image. This real image is the object for the second lens, called the eyepiece lens, and is placed just inside the focus of the eyepiece lens. The final image formed is magnified, virtual, still inverted and formed far away from the eyepiece lens so that the it can be viewed with a relaxed eye.
OB42 identify, and understand the functions of, the main parts of a microscope (light microscope only) and use it to examine an animal cell and a plant cell
Parts of the Microscope
Eyepiece Lens: magnifies the image produced by the objective lens. The usual level of magnification is 10X (magnified to make it look ten times bigger) The magnification is marked on the lens.
Nosepiece: allow different levels of magnification by allowing easy change to a different objective lens.
Objective Lens: magnifies the image of the object under study; the level of magnification is engraved onto the lens casing e.g. 4X, 10X, 40X. The 4X is the low power and the 40X the high power objective lens.
Coarse Focus Wheel: used for focusing at low power when using the low power objective lens.
Fine Focus Wheel: used for exact clear focusing producing the sharpest image at all levels of magnification; this is the only focus wheel to use with the medium and high power objective lens!
Stage: the glass slide is placed on the stage with the object for study it carries placed directly over the hole in the stage so light can pass through it; clips on the stage may be used to hold the slide in a steady position.
Light Source: this may be a reflecting mirror or a lamp below the stage.
Condenser: focuses the light from the light source onto the object on the slide.
Diaphragm: used to vary the amount of light passing to the object to get an image of the best clarity – not too bright or too dark.
The amount of magnification a microscope generates is found by multipling the magnification of the eyepiece by the magnification of the objective lens
OB44 prepare a slide from plant tissue and sketch the cells under magnification
How to use a microscope
When moving your microscope, always carry it with both hands.
Grasp the arm with one hand and place the other hand under the base for support.
Do not touch the glass part of the lenses with your fingers.
Use only special lens paper to clean the lenses.
Always keep your microscope covered when not in use. Dust is the number 1 enemy!
Investigation:Using the Microscope to Examine Animal and Plant Cells
1. Turn the revolving nosepiece so that the lowest power objective lens is "clicked" into position (This is also the shortest objective lens).
2. Switch on light or adjust the mirror to get good light.
3. Place a prepared glass slide, of plant or animal cells onto the stage.
Your microscope slide should be prepared with a coverslip or cover glass over the specimen. This will help protect the objective lenses if they touch the slide. Place the microscope slide on the stage and fasten it with the stage clips. You can push down on the back end of the stage clip to open it.
4. Make sure that the tissue is centred directly above the hole in the stage.
The proper way to use a monocular microscope is to look through the eyepiece with one eye and keep the other eye open (this helps avoid eye strain). If you have to close one eye when looking into the microscope, it's ok. Remember, everything is upside down and backwards. When you move the slide to the right, the image goes to the left!
5. Turn the coarse focusing wheel to bring the lens as close to the slide as possible.
6. Look through eyepiece and turn coarse focusing knob to slowly move lens away from slide until the tissue is in focus.
Slowly turn the coarse adjustment so that the objective lens goes up (away from the slide). Continue until the image comes into focus. Use the fine adjustment, if available, for fine focusing. If you have a microscope with a moving stage, then turn the coarse knob so the stage moves downward or away from the objective lens.
7. The diaphragm may have to be used to change the brightness to give a better view.
8. Observe the cells and move the slide side to side to scan the tissue. Sketch what you see.
9. Before increasing the magnification, move the area of greatest interest into the very centre of your view.
10. Click the next higher objective lens, the medium power, (10x) into position.
11. Only turn the fine focusing wheel to sharpen the image.
12. Note the greater detail – draw a labelled diagram of part of a cell.
13. Before increasing the magnification, move the area of greatest interest into the very centre of your view.
14. Click the high power objective lens (40X) into position, draw a labelled diagram of a plant or animal cell. Only turn the fine focusing wheel to sharpen the image.
15. When finished, raise the tube (or lower the stage), click the low power lens into position and remove the slide.
A microscope can allow us to see down to the size 10-6m, a micron!
What to observe with your own microscope ....
http://www.funsci.com/texts/enom.htm
http://www.microscopy-uk.org.uk/ponddip/index.html
Some close up's of cells
http://cellpics.cimr.cam.ac.uk/index.html
the Journal of Cell Biology has a website to access a vast database of perfect slides
http://jcb-dataviewer.rupress.org/
Brownian motion
http://galileoandeinstein.physics.virginia.edu/more_stuff/Applets/brownian/brownian.html
Online Digital Microscope