The equation that relates the power of a lens to its focal length is:
power (in dioptres)=1focal length (in metres) \text{power (in dioptres)} = \frac{1}{\text{focal length (in metres)}} power (in dioptres)=focal length (in metres)1The power of a magnifying lens is 8 dioptres8\text{ dioptres}8 dioptres.
Use the equation to calculate the focal length of this lens in cm\text{cm}cm.
24 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.