An IGCSE student is using optics pins to trace the path of light through a rectangular glass block. The student places two pins, P1 P_1\,P1 and P2P_2P2, on the incident ray. The student then looks through the opposite side of the block to place two pins, P3 P_3\,P3 and P4P_4P4, in line with the images of P1 P_1\,P1 and P2P_2P2.
State why the student should place the pins P1 P_1\,P1 and P2 P_2\,P2 as far apart as possible, and state the minimum recommended distance between them.
The pins might not be pushed into the paper perfectly vertically. Explain how the student can align the pins P3 P_3\,P3 and P4 P_4\,P4 with the images of P1 P_1\,P1 and P2 P_2\,P2 as accurately as possible.
In a trial, the student measures an angle of incidence at the first boundary of i=35∘i = 35^\circi=35∘ and an angle of refraction inside the block of r=22∘r = 22^\circr=22∘.
Calculate the refractive index n n\,n of the glass block to two decimal places.
State the unit of the refractive index, if any.
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.