Calculating magnification from image and object sizes or distances, applying 1/f = 1/u + 1/v with a sign convention, and methods to find the focal length of a converging lens.
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 scale diagram is a good guide, but a formula gives the exact answer. With the lens formula you can predict where the screen must go.
Narration uses your device’s built-in voice. No sound? Switch to “Captions only” — the captions advance on their own.
Copy these into your notebook in your own words — that is how they stick.
m = h_i/h_o = v/u; no unit.
1/f = 1/u + 1/v.
Real: positive distances; virtual image: v negative.
f positive; concave lens: f negative.
v positive; inverted.
v negative; upright; magnifying glass when u < f.
Image of a far object forms at the focal plane: v ≈ f.
f = uv ÷ (u + v).
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 10.0 cm forms an image of a 6.0 cm tall object placed 25.0 cm from the lens.
(a) (a) State the lens formula and define each symbol. [3]
(b) (b) Calculate the image distance. [3]
(c) (c) Calculate the magnification. [2]
(d) (d) Calculate the height of the image. [2]
(e) (e) State two characteristics of the image. [2]
(f) (f) Describe one method to find the focal length of the lens in the laboratory. [3]
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.