A student is investigating the reflection of light using a plane mirror, a ray-trace sheet, and optical pins. They draw a line XYXYXY on the sheet to represent the front surface of the mirror, and draw a normal NPNPNP at the midpoint PPP. An incident ray is drawn at an angle of i=40∘i = 40^\circi=40∘ to the normal, and a pin P1P_1P1 is placed on this ray at a distance of 8.5 cm8.5\text{ cm}8.5 cm from PPP.
Pin Placement: (i) State the minimum recommended distance between pin P1P_1P1 and a second pin P2P_2P2 on the same ray line. (ii) Explain why keeping a large distance between the pins improves the accuracy of the drawn ray.
Precautions: State two practical precautions that the student should take when placing the pins or aligning their images to ensure reliable results.
Experimental Error: Even with careful alignment, the student notices a small systematic error where the constructed reflected ray does not perfectly match the theoretical expectation i=ri = ri=r. Suggest a practical reason related to the construction of a typical glass mirror that explains this discrepancy.
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.