A student investigates the image formed by a converging lens.
The student sets up the apparatus with a screen placed at a distance D=90.0 cmD = 90.0\text{ cm}D=90.0 cm from an illuminated, upright triangular object. Two positions of the lens produce a sharp image on the screen:
(i) Describe how the second image (at Position 2) differs in appearance (orientation and relative size) from the original upright triangular object.
(ii) Calculate the distance d=Y−Xd = Y - Xd=Y−X.
(iii) Calculate the focal length f1f_1f1 of the lens using the equation:
f=D2−d24D f = \frac{D^2 - d^2}{4D} f=4DD2−d2Give your answer to 3 significant figures.
The student repeats the procedure for an object-to-screen distance D=100.0 cmD = 100.0\text{ cm}D=100.0 cm. The student records:
X=20.3 cm X = 20.3\text{ cm} X=20.3 cm Y=79.7 cm Y = 79.7\text{ cm} Y=79.7 cm(i) Calculate the new distance ddd for this setup.
(ii) 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 equal within the limits of experimental accuracy if their values are within 10%10\%10% of each other. State whether your values of f1f_1f1 and f2f_2f2 can be considered equal. Support your statement with a calculation.
(i) State one technique to use when doing this type of experiment to ensure that the image on the screen is focused as clearly as possible.
(ii) Explain why this experiment is usually done in a darkened room.
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.