# University of New Zealand. — Physical Science. — Paper c. Electricity and Magnetism

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## Paperc. Electricity and Magnetism.

 1 Describe the construction of a simple ordinary electric machine, and explain its action in conformity with the doctrines of energy, without having recourse either to the language or the ideas of the old two-fluid theory. 2 If a disk of copper or any metal is set in rotation beneath a suspended compass-needle, the needle is observed to turn in the sense of the rotation. Explain this. 3 A copper tube rotated between the poles of a powerful magnet is observed to grow warm. Explain this. 4 A bundle of thin wires of soft iron is hung by a long thin thread horizontally, and makes an angle of 45° with the plane of a coil of fine wire, whose aperture is horizontal, and which surrounds the bundle. On sending through the coil the rapidly alternating currents generated in the secondary wire of an induction-coil the bundle is observed to be deflected to a greater angle. Explain this.page 2 5 Give an account of a method of determining the horizontal component of the earth's magnetic field. 6 State the principal laws of electrodynamics, and show by applying the principle of the conservation of energy, that if two conductors carrying concurrent currents attract one another, a non-concurrent current will be generated in a conductor (closed on itself) which is moved towards a conductor which already carries a current. 7 Give Ampère's rule for the mutual reaction between a current and a magnet pole. Sketch the lines of force of the magnetic field due to an indefinitely long straight conductor; and calculate the force it exerts on a unit-pole at distance =a when traversed by a current=i. 8 What is an electromagnet? What rule can you give for the amount of magnetism evoked in an electromagnet by currents of different strengths? An electromagnet having many turns of thick wire is introduced into a simple circuit along with a galvanometer, a battery, and a key. Discuss the actions occurring on making the circuit and on breaking the circuit. 9 What is a condenser? A condenser is placed in a simple circuit along with a galvanometer having many turns of fine wire, a battery of cells, and a key. Discuss the actions occurring on making connexion and on breaking connexion. 10 Explain the connexion existing between the heat of combustion of a metal, its electrochemical equivalent and its position in the volta-electric series.