Preparing a slide Before you can use the microscope, you will first have to mount the object you want to look at on a glass slide, in a drop of water or stain and cover with a cover-slip.
This can easily be done as follows: 1. Place the object you want to look at on the centre of a glass slide. 2. Use a dropper to cover the object with about three drops of water or stain. 3. Leave the stain for one minute and rinse off excess with water. 4. Using a mounted needle, hold a cover-slip at the edge of the water at an angle of 45°. 5. Gently lower the cover-slip to cover the object, to avoid trapping air bubbles.
Activity Using a light microscope
1. Plug in the light or adjust the mirror underneath so that light is seen when you look through the eyepiece lens.
2. Place the glass slide on the stage so that what you want to look at is over the centre of the hole on the stage.
Objective lens
3. With the low power objective lens in position, watch from the side and turn the coarse focus knob to lower the objective lens close to the slide, without touching it. Warning! Do not allow the lens to touch the slide – the objective lens is easily damaged!
Stage
Coarse focus knob
Fine
focus knob
4. Look through the eyepiece and very slowly turn the coarse focus knob the opposite way to the way you turned it in Step 3. This raises the objective lens.
Fig. 3 Using a microscope.
5. The object you are looking at should now become visible. You may need to move the slide very slightly on the stage in order to centre it perfectly. Use the fine focus knob to improve the visibility of the image.
6. When using the medium power (×10) objective lens or the high power (×40) lens, never use the coarse focus knob – only the fine focus knob.
Note Using the microscope to get the best results takes practice! Try examining a hair, a speck of dust and a piece of newspaper under the microscope. You will first have to mount the object on a slide and cover it with a cover-slip, as described.
Science in Society Investigate the different types of microscopes used in science today. Which ones are the most powerful and what do they display? Where are these microscopes used?
