How converging and diverging lenses act on a beam of parallel rays, the key terms (principal axis, principal focus, focal length, focal plane), and ray diagrams for real and virtual images.
5 narrated scenes. Press play, listen and read along — the points appear as they are explained. Use ‹ Prev / Next › or the scene bar to jump to any scene.
A camera, a magnifying glass and the lens of your own eye are all just shaped pieces of glass or tissue bending light. A ray diagram shows how.
Narration uses your device’s built-in voice. No sound? Switch to “Captions only” — the captions advance on their own.
Move the object and see how the image changes.
Copy these into your notebook in your own words — that is how they stick.
Converging; thick in the middle; real focus.
Diverging; thin in the middle; virtual focus.
Line through the centre of the lens at right angles to it.
Where rays parallel to the axis meet (convex) or appear to come from (concave).
Distance from the optical centre to F.
Plane through F at right angles to the axis.
Formed on a screen; inverted.
Cannot be formed on a screen; upright; same side as the object (convex, object within F).
3 quick games on this lesson. Earn XP and badges as you play — your best score for each game is saved. Games are for practice and do not change your exam readiness. More games in the Physics Arcade.
8 items modelled on real CSEC Paper 1 questions. Choose one answer for each, then check. Aim for 80% or better. Work each item on paper first.
Write full answers, then reveal the mark scheme and tick the points you earned (15 marks in total). Show all your working — method marks count. Your answers are saved on this device.
Question 1 [15 marks]
A convex lens of focal length 6.0 cm is used to form an image of an object placed 15 cm in front of it.
(a) (a) Define the principal focus of a convex lens. [2]
(b) (b) Draw a ray diagram, to scale, to show the formation of the image. [4]
(c) (c) State the nature of the image (real or virtual, upright or inverted, magnified or diminished). [3]
(d) (d) State one use of this arrangement. [1]
(e) (e) State the characteristics of the image if the object is moved to 4.0 cm from the lens. [3]
(f) (f) Distinguish between a real and a virtual image. [2]
Find these in your own past-paper booklets for extra timed practice. Items above are written in the style of these papers; any adapted from a specific question say so.