Brainlag PlusConvex and concave lenses, ray diagrams, real and virtual images, and magnification = image height ÷ object height.
Two kinds of lens
A lens refracts light to form an image.
- A convex (converging) lens is fatter in the middle. Rays parallel to the axis are brought together at the principal focus F.
- A concave (diverging) lens is thinner in the middle. Parallel rays spread out as if they came from a principal focus on the near side.
- The focal length is the distance from the centre of the lens to F. A shorter focal length means a more powerful lens.
In diagrams a convex lens is a line with outward arrowheads, a concave lens a line with inward ones.
The rest of this lesson and its 10 practice questions are in Plus.
Screen 1 of 5, free to read.
- 10 exam-style questions, marked as you go, each with a worked solution
- The Lenses simulation beside every question
- Anything you get wrong is saved to your flashcards