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waves from any direction. The device is known as an oscillating
water column. As a wave rises, air is pushed through an air
turbine and sucked back again as the wave falls.
The turbine has been designed by Professor Alan Wells, of
Queen’s University, Belfast. It will generate 2 megawatts. There is
potential for 300 Ospreys in Scottish waters, which could provide
10 percent of the country’s peak electricity demand.

LESSON 7

SUMMARY OF IMPORTANT FACTS

1. Principles of Electricity

A chemical element is built up from atoms. Each atom is
made up of electrons, protons and neutrons. The electron has a
negative charge and the proton a positive charge; the two electrical
charges are equal and opposite, but the mass of proton is 1840
times greater than that of the electron. Current flow is a
combination of electron flow (negative charge carries) and hole
flow (positive charge carries).
A conductor offers low resistance to current flow, an
insulator offers high resistance. The resistance of semiconductor is
mid-way between the two extremes.
Voltage or e. m. f. is a measure of the potential of an electric
circuit to produce current flow. The conductance (G) of an
electrical circuit is measured in simians (S) and resistance (R in
ohms).
A linear circuit element is one whose resistance is constant
despite fluctuations of voltage and current. The resistance of a
non-linear circuit element varies with fluctuations of voltage and
current. A direct current or unidirectional current always flows in
the same direction around a circuit. An alternating current
periodically reverses its direction of flow if the periodic time of an

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