An IGCSE student is determining the focal length of a lens.
The student records two sets of readings for the object distance xxx (the actual distance from the illuminated object to the centre of the lens) and the image distance yyy (the actual distance from the centre of the lens to the screen).
For the first set of readings, the student makes measurements on a scale diagram of the experimental set-up. The diagram is drawn to 14\frac{1}{4}41 (one-quarter) of the actual size. On this diagram:
For the second set of readings, the student records the actual distances directly in the laboratory:
Calculate the actual distance xxx and the actual distance yyy for the first set of readings.
Calculate the focal length fff of the lens for both sets of readings using the equation:
f=xyx+y f = \frac{xy}{x + y} f=x+yxyRecord your values of fff to an appropriate number of significant figures (at least 3 significant figures).
Calculate the average value of the focal length of the lens.
State two precautions you would take in the laboratory in order to obtain reliable measurements.
216 exam-style questions on CIE IGCSE Physics 3.2 Light, covering 3.2.1a Reflection of light, 3.2.1b Images in a plane mirror, 3.2.2 Refraction of light, 3.2.2a Refraction of light, 3.2.2b Total internal reflection, 3.2.2c Refractive index and critical angle, 3.2.2d Optical fibres, 3.2.3a Converging and diverging lenses, 3.2.3b Ray diagrams and the nature of images, 3.2.3c Virtual images and the magnifying glass, 3.2.3d Correcting long-sightedness and short-sightedness, and 3.2.4 Dispersion of light. Each one has a worked solution and a mark scheme showing where the marks go.