section 1: cell structure - topic 5: using microscopes

Question 1

how to use a light microscope?

Answer 1

1. start by clipping the slide containing the specimen onto the stage.
2. select the lowest-powered objective lens i.e. the one that produces the lowest magnification.
3. use the coarse adjustment knob to bring the stage up to just below the objective lens.
4. look down the eyepiece (which contains the ocular lens). use the coarse adjustment knob to move the stage downwards - away from the objective lens - until the image is roughly in focus.
5. adjust the focus with the fine adjustment knob, until you get a clear image of what’s on the slide.
6. if you need to see the slide with greater magnification, swap to a higher-powered objective lens and refocus.

Question 2

what is an eyepiece graticule?

Answer 2

it’s fitted onto the eyepiece.
it’s like a transparent ruler with numbers, but no units.
so when you look through the eyepiece, you’ll see a scale.

Question 3

what is a stage micrometer?

Answer 3

this is placed on the stage.
it is a microscopic slide with an accurate scale (it has units) and it’s used to work out the value of the divisions on the eyepiece graticule at a particular magnification.

Question 4

why are the EG & SM helpful?

Answer 4

because it means when you take the stage micrometer away and replace it with the slide containing your specimen, you’ll be able to measure the size of the specimen.

this works because you’ll have worked out what lengths the divisions on your eyepiece graticule actually represent.