A student template for investigating the refraction of light through a transparent rectangular block is prepared on a sheet of paper.
The student draws the outline of the block ABCDABCDABCD. A normal NN′ NN'\,NN′ is drawn passing through the top side AB AB\,AB at point F F\,F and the bottom side CD CD\,CD at point GGG. An incident ray path EF EF\,EF is drawn at an angle of incidence i=30∘i = 30^\circi=30∘ to the normal.
After placing the block, the student places two pins P1 P_1\,P1 and P2 P_2\,P2 on the line EFEFEF. Looking through the opposite side CD CD\,CD of the block, she aligns two more pins P3 P_3\,P3 and P4 P_4\,P4 with the images of P1 P_1\,P1 and P2P_2P2.
She then removes the block, draws a straight line through the positions of P4 P_4\,P4 and P3 P_3\,P3 and extends it to meet the side CD CD\,CD at point HHH. Finally, she draws the line HFHFHF.
The student measures the length a a\,a of the line GH GH\,GH to be 14 mm and the length b b\,b of the line HF HF\,HF to be 42 mm.
Calculate the refractive index n n\,n of the material of the block using the equation:
n=b2a n = \frac{b}{2a} n=2abSuggest how far apart the student should place the pins P3 P_3\,P3 and P4 P_4\,P4 on the ray trace sheet.
State a reason for your suggestion in (b)(i).
The experiment can also be carried out using a ray of light produced by a ray box instead of using optical pins.
Assuming both methods are performed carefully: Suggest one source of inaccuracy when using the optical pin method.
Suggest one source of inaccuracy when using the ray box method.
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.