# University of New Zealand. — Physical Science. — Paper b (1). Sound and Light

page break

## Paperb (1). Sound and Light.

 1 What do you know of partial tones? How is their existence in the note of a musical instrument demonstrated? What part do they play in the theory of consonance and dissonance? 2 Discuss the reflexion of waves of condensation and of rarefaction at the end of a tube through which the wave has been transmitted, (a) when the end of the tube is stopped, (b) when it is open. Deduce the laws connecting the frequency of the notes of stopped and of open organ-pipes with their lengths. 3 Give some account of the optical method of tuning. 4 Describe the phenomena of phosphorescence and fluorescence, distinguishing carefully between the two. Explain Becquerel's method of applying phosphorescent bodies to investigate the infra-red region of the spectrum. 5 State the laws of refraction of light, and explain them briefly in accordance with the wave-theory. Give Huygens' construction for a refracted ray.page 2 6 Light passes from a medium whose refractive index is μ to one whose index is μ', through a surface whose radius of curvature is r. Suppose the focus of the incident pencil to be at distance x from the centre of curvature of the surface, calculate the distance of the focus of the refracted pencil from the same point. 7 Describe the necessary arrangements for obtaing a pure spectrum, the source of light being a narrow slit in front of a luminous object. State and explain the differences that exist between the spectrum as produced by a prism and that produced by a grating. 8 How is the index of refraction of an opaque solid measured? What is the relation between the refractive index of a substance and the percentage of light which it reflects (at perpendicular incidence) at its surface? 9 Explain the phenomenon of the rainbow, and in particular show (1) why the colours of the secondary bow are in reverse order to those of the primary, (2) why the space between the two bows is darker than the rest of the sky, (3) why we do not see the Fraunhofer lines in the rainbow.