What it does
A light microscope uses two lenses: the eyepiece you look into and the objective close to the slide. Each one magnifies, so the total magnification = eyepiece × objective. This page draws the view down a school microscope. Pick a slide (onion peel, cheek cells or pond water), choose the 4×, 10× or 40× objective, turn the focus knob until the picture is sharp, set the light, and add a stain to bring out the nucleus. Drag the picture to move the slide around, just as you would push the slide on the stage.
It follows the school topics Class 8 Science, the invisible living world (using a microscope, cells and microorganisms) and Class 9 Biology, the fundamental unit of life (plant and animal cells). After looking at real-looking cells, the cell explorer labels each part of a cell, and microscope and telescope shows how the two lenses form the image with ray diagrams.
How to use it
- Choose a slide.
- Start with the 4× objective. Move the focus knob slider until the line under the picture says “in focus”.
- Switch to 10×, then 40×. You only need a small turn of the focus knob each time, and at 40× the picture goes blurry with the slightest turn.
- Tick Add a stain: iodine for onion peel (brown nucleus), methylene blue for cheek cells (blue nucleus).
- Lower the light to see why a bright, even lamp matters.
- Drag the picture to explore. The scale bar at the bottom shows how big things really are.
The Level switch (Class 9 and up) adds the field of view (how wide the circle is on the slide) and a ruler: choose “Drag measures” and drag across a cell to read its real size in micrometres (1 µm = 1/1000 mm).
Worked example
With the 10× eyepiece and the 40× objective, total magnification = 10 × 40 = 400×. The field of view is the field number divided by the objective: 18 mm ÷ 40 = 0.45 mm, which is 450 µm. An onion cell that stretches across about half the circle is therefore about 225 µm long. With the 4× objective the total is 40× and the field of view is 18 ÷ 4 = 4.5 mm, ten times wider, so you see many more cells, each one smaller.
If a drawing of a cell is 12 mm wide at 400×, its real width is 12 ÷ 400 = 0.03 mm = 30 µm.
Check yourself
Five fresh questions: total magnification, how the field of view changes with the objective, real size from a drawing, which lens to start with, and why we stain. Nothing is saved.
Tips
- Always focus at low power first, then move up. The view is wider and easier to find.
- Plant cells look like bricks with thick walls; animal cells are rounder with thin edges and no wall.
- Things that move in pond water are alive. Bacteria are so small that even at 400× they are only dots.
FAQ
Why does the picture get darker at high power? A strong objective gathers light from a smaller area, so you often need more light at 40×. On this page the light slider shows the effect.
Are these real photographs? No. The page draws the specimens with rounded sizes so they look like what you would see, without copying any images.
Is this from NCERT? No. It is an independent study aid that follows the same school topics, with its own drawings and numbers.
Where the numbers come from
- Total magnification = eyepiece × objective, field of view = field number ÷ objective magnification, real size = image size ÷ magnification: standard school microscopy. The field number of 18 mm is a typical round value for school eyepieces.
- Specimens are drawn by the page with rounded, typical sizes (onion cells a few hundred micrometres long, cheek cells about 60 µm, paramecium about 200 µm); no photographs or textbook figures are used.
- Checked by hand: total magnification and field of view for every lens choice, and the ruler line against the scale bar.
Standard scientific values, such as constants, atomic weights and melting points, are facts found in every textbook; we name where ours were checked. If you are an author or publisher and want a value, a credit or a table changed or removed, tell us and we will act quickly.
Last updated 2026-11-09.