An experiment is set up to determine the focal length f f\,f of a converging lens using an illuminated object, a lens, and a screen.
Describe a technique for obtaining an image on the screen that is as sharp as possible.
The height of the illuminated object is hO=3.0 cmh_O = 3.0\text{ cm}hO=3.0 cm. When the object distance u u\,u is set to a certain value, the height of the sharp image on the screen is measured to be hI=4.8 cmh_I = 4.8\text{ cm}hI=4.8 cm. Calculate the value of W W\,W using the formula:
W=hOhI W = \frac{h_O}{h_I} W=hIhOGive your answer to 2 decimal places.
The experiment is repeated for several different object distances uuu. A graph of u / cmu\text{ / cm}u / cm (y-axis) against WWW (x-axis) is plotted. The student identifies two points on the resulting line of best fit: (0.60,24.0 cm)(0.60, 24.0\text{ cm})(0.60,24.0 cm) and (3.00,60.0 cm)(3.00, 60.0\text{ cm})(3.00,60.0 cm). Determine the gradient G G\,G of this line. Show your working.
The focal length f f\,f of the lens is numerically equal to the gradient GGG. State the value of f f\,f in cm\text{cm}cm.
The student decides to continue the experiment using much larger values of uuu. Explain why this produces less accurate values for WWW.
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.