A lens gathers light into a focus
A parallel beam of rays passes through a converging lens and meets at one point — the focus. Then try a diverging lens.
2D
Age 10+10 min
Light & optics
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Press “Run”. Bodies move by the laws of physics: gravity, friction, elasticity.
What the experiment shows
The laser makes a wide parallel beam. A convex lens bends the rays so that they all cross the axis at the focal distance f behind the lens.
How to run it
- Find the focal dots on the axis: the rays meet at the right one.
- Select the lens and change the focal length — the focus moves.
- Set a negative f: the beam becomes diverging.
Questions to discuss
- How do a magnifying glass and reading glasses work?
- Why does a more strongly curved lens give a shorter f?
The science
A thin lens deflects a ray that crosses it at height h from the axis by an angle ≈ h/f, so all parallel rays meet at distance f. Optical power D = 1/f (in dioptres when f is in metres).
Try it at home
Catch the Sun with a magnifying glass on a sheet of paper and measure the distance to the smallest spot — that is the focal length.
What to change in the editor
- Change the beam width.
- Add a second lens.