An optical alignment device uses a lens to spread parallel rays of light. Its lens needs replacing.
The replacement must:
The table gives data for three available lenses.
| Lens | Magnitude of focal length in cm | Shape |
|---|---|---|
| A | 18 | thinner at the centre than at the edges |
| B | 14 | thinner at the centre than at the edges |
| C | 13 | thicker at the centre than at the edges |
Calculate the power of each lens in dioptres.
Use P=1fP=\dfrac{1}{f}P=f1, where f f\,f is in metres.
Give each answer to 2 significant figures.
Explain which lens should be used as the replacement.
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.