Laboratory work: determining the refractive index of glass
The aim is to measure the refractive index of a glass prism. We direct a thin beam perpendicular to a side face of the prism: it is not refracted at the first face and goes straight inside the prism, reaching the second face at an angle of incidence equal to the prism’s apex angle α. On leaving the second face into air the ray is refracted and deviates from its original direction by the angle γ; the angle of refraction is then α + γ. From the law of refraction n sin α = sin(α + γ), i.e. n = sin(α + γ)/sin α. We mark the ray path before and after the prism with two pins each and measure γ with a protractor. The experiment is repeated 3 times and the mean n is taken. Pins are sharp: use them only as the teacher shows, under adult supervision, away from your face; never connect the lamp’s electric supply yourself.
Make a table: experiment number, α, γ, α + γ, sin α, sin(α + γ), n. Find the mean n from three measurements and compare it with 1.5. Discuss the sources of error: crooked pins and the precision of angle measurement.