A student is investigating the image formed by a converging lens using an optical bench setup.
They place an illuminated object at a distance u=18.2 cmu = 18.2\text{ cm}u=18.2 cm from the lens, and adjust the position of a screen on the other side of the lens until a sharply focused image of the object is formed. The distance from the lens to the screen is measured as v=45.5 cmv = 45.5\text{ cm}v=45.5 cm.
Calculate the focal length fff of the lens using the equation:
f=uvu+v f = \frac{uv}{u+v} f=u+vuvGive your answer to a suitable number of significant figures for this experiment, including the unit.
State two precautions you would take in the laboratory in order to obtain reliable measurements when carrying out this experiment.
The object used is an illuminated arrow pointing upwards. Suggest two differences between the appearance of the illuminated object and the well-focused image on the screen.
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.