Ray Diagrams & Images
Construct ray diagrams to show the formation of images by plane mirrors and converging lenses, identifying whether images are real or virtual, magnified or diminished, upright or inverted
What a learner can do afterwards
- Draws an accurate ray diagram for a plane mirror showing a virtual, upright, same-size image
- Draws a ray diagram for a converging lens to show image formation
- Uses a ray diagram to determine whether the image is real or virtual and which side of the lens it forms
- Applies ray diagram knowledge to explain how glasses, cameras, or projectors work
The lesson
You've learned that light reflects off mirrors and refracts through lenses. A ray diagram uses straight lines to trace exactly where that light goes, so you can find where an image forms and what it looks like.
For a flat mirror, two rules always hold. The image is virtual, meaning the light doesn't actually meet there, it only seems to. And the image is upright and exactly the same size as the object, sitting as far behind the mirror as the object stands in front of it.
Stand 1 metre from a bathroom mirror. Rays of light from your face bounce off the glass and travel to your eyes. Your brain traces those rays backward in straight lines, right through the mirror, and 'sees' you standing 1 metre behind the glass. No light is really there, so the image is virtual.
A converging lens bends light instead of bouncing it. Two rays are enough to trace the image. One ray travels parallel to the axis, then bends through the focal point on the far side. Another ray passes straight through the lens's center, with no bend at all. If the object sits beyond the focal point, the two rays actually cross past the lens. That makes a real image, upside down, which you could catch on a screen. If the object sits closer than the focal point, like a magnifying glass over a word, the rays never truly cross. They only seem to meet back on the object's side, giving a virtual, upright image that looks bigger. A virtual image can never land on a screen, because no light actually gets there.
A plane mirror always gives a virtual, upright, same-size image; a converging lens gives either a real, inverted image or, held close, a virtual, upright, magnified one.
Watch it
Where it sits
Learn first
This opens up
Nothing builds on it yet.
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.