A machine uses a converging lens with a focal length of 14 cm to form an image of a small illuminated symbol.
An engineer carries out two tests using the same lens.
| Test | Distance from the symbol to the lens in cm\mathrm{cm}cm |
|---|---|
| 1 | 9 |
| 2 | 21 |
A light-sensitive screen can be moved along the principal axis on the opposite side of the lens from the symbol.
Explain which test can produce a sharp image on the screen and why the other test cannot.
93 exam-style questions on Edexcel GCSE Physics 5.1 Reflection, refraction and lenses, covering 5.1.1 Reflection, refraction and total internal reflection, 5.1.2 Specular and diffuse reflection, 5.1.3 Colour of light: absorption and filters, 5.1.4 Lenses: power, focal length and shape, 5.1.5 Ray diagrams for converging and diverging lenses, and 5.1.6 Real and virtual images. Each one has a worked solution and a mark scheme showing where the marks go.