A student performs a ray-tracing experiment to determine the refractive index of a transparent rectangular block.
The student draws a normal at the centre of side ABABAB of the block, meeting the side at point EEE. Point NNN is marked on the normal outside the block such that EN=5.0 cmEN = 5.0\text{ cm}EN=5.0 cm. A straight line NFNFNF representing the incident ray is drawn to the block at an angle of 25∘25^\circ25∘ to the normal, where FFF lies on ABABAB.
Calculate the length aaa of the line NFNFNF. Give your answer to 2 significant figures.
In the experiment, the student traces the ray through the block and out the other side. By extending the refracted ray, they find it meets the normal at point HHH inside the block. The measured length bbb of the line FHFHFH is 7.6 cm7.6\text{ cm}7.6 cm. Calculate the refractive index nnn of the block using the formula:
n=ba n = \frac{b}{a} n=abGive your answer to 2 significant figures.
Suggest two precautions that should be taken in this pin-tracing experiment to obtain readings that are as accurate as possible.
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.