A student investigates the image formed by a converging lens.
The student sets up the apparatus such that:
The student then continues to move the lens further away from the illuminated object until a second sharp image, which is diminished and inverted, is formed on the screen. The actual object distance is now Y=66.5 cmY = 66.5\text{ cm}Y=66.5 cm.
(i) Describe the appearance of the second sharp image formed on the screen in terms of its orientation and relative size compared to the original object. (ii) Calculate the value of d=Y−Xd = Y - Xd=Y−X. (iii) The focal length f1 f_1\,f1 of the lens can be found using the equation:
f1=D2−d24D f_1 = \frac{D^2 - d^2}{4D} f1=4DD2−d2Calculate the value of f1f_1f1. Give your answer to 3 significant figures.
The student repeats the procedure for an object-to-screen distance D=110.0 cmD = 110.0\text{ cm}D=110.0 cm and records the following results:
Calculate a second value, f2f_2f2, for the focal length of the lens using the same equation. Give your answer to 3 significant figures.
Two quantities can be considered to be equal within the limits of experimental accuracy if their values are within 10% of each other. State whether your values of f1 f_1\,f1 and f2 f_2\,f2 can be considered equal. Support your statement with a calculation.
This experiment is usually performed in a darkened room. Explain how this makes it easier to determine when the image is in sharp focus.
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.