Theory & Modules
Bite-sized modules with labelled diagrams, observations, and exam tips. Each module embeds the same physics engine that powers the main lab.
- A ray incident at the optical centre O passes undeviated.
- A ray parallel to the principal axis, after refraction, passes through F₂ (convex) or appears to come from F₂ (concave).
- A ray through F₁ (convex) or directed towards F₁ (concave), emerges parallel to the principal axis.
Only two of the three rays are needed to locate the image — the third is a useful check.
At infinity (object very far)
Image at F₂ · highly diminished · real & inverted.
Burning Glass
Beyond 2F₁
Image between F₂ and 2F₂ · diminished · real & inverted.
Camera Lens
At 2F₁
Image at 2F₂ · same size · real & inverted.
Terrestrial Telescope
Between F₁ and 2F₁
Image beyond 2F₂ · magnified · real & inverted.
Slide Projector
At F₁
Image at infinity · highly magnified · real & inverted.
Spectrometer
Between F₁ and O
Image on same side · virtual · erect · magnified.
Magnifying Glass