Proceedings of the Technical Session of Institute of Physics, Sri Lanka 7 (1991) c1

Posible Evidence For "Paddle Wheel Mechanism" for Ionic Transport in a-Li₂so₄
M.A. Careem, M.A.K.L. Dissanayake, P.W.S.K. Bandaranayake  & C.N. Wijayasekara
Department of Physics, University of Peradeniya, Peradeniya.

a-Li2SO4 is a stable solid electrolyte above 577⁰C with a high ionic conductivity of the order of 1 ohm-1cm-1. This high conductivity may be attributed to an unusual transport mechanism called "paddle wheel mechanism" where the mobility of the Li⁺ ions is strongly enhanced by the partial rotational motion of the transitionally static sulphate ions (1). The effect on the ionic conductivity of a-Li₂SO₄ on adding small amounts of Li₂WO₄ was investigated by measuring  the electrical conductivities of various compositions of Li₂SO₄ + Li₂WO₄ system at temperatures above 577⁰C using the U-cell technique. The electrical conductivities for compositions with 2-2.5 mole percent of Li₂WO₄ within the solid solubility region in the a-phase were found to be slightly lower than those of pure a-Li₂SO₄ at corresponding temperatures. This is in contrast to the conductivity enhancement observed in the same system in the monoclinic b-phase at temperatures below the phase transition (2). The lowering of the ionic conductivity of a-Li₂SO₄ due to Li₂WO₄ doping can be interpreted in favor of the 'paddle wheel' type of mechanism for the high ionic transport in a-Li₂SO₄.

Proceedings of the Technical Session of Institute of Physics, Sri Lanka 7 (1991) c2

The Effects of Noise on Man
L.P.J.P. Premaratne
Department of Physics, University of Moratuwa, Moratuwa

Sound intensity is the acoustical energy measured in Watts per square meter. Sound intensity level or simply the sound level, is the sound intensity measured in decibels (dB). The safe range for the unprotected ear is 0-85 dB. The threshold of discomfort occurs around 120 dB.

The unwanted sound or noise is a nuisance. There are permissible noise exposure limits. Long - exposure to noise is a health hazard and can give rise to undesirable effects such as temporary threshold shift, permanent threshold shift or noise - induced deafness.

Noise is a growing problem in the environment and in particular in some occupations. Related data is presented to investigate the situation in Sri Lanka in this regard. The local standards are presented and compared with those of some other countries.

Noise is transmitted from a source to a receiver. To control noise, therefore, we can reduce the source, interrupt the path of transmission or protect the receiver. The necessity is, to realize that noise control is important for good health and peaceful living of man.

Proceedings of the Technical Session of Institute of Physics, Sri Lanka 7 (1991) c3

Construction of a Hydrometer to Investigate the Variations in Relative Humidity
A.P.P.M. Jayasekara
Department of Physics, University of Kelaniya, Kelaniya

'Wet and Dry bulb' Thermometer principle is used to design a Hydrometer which is capable of monitoring of the continuous variations in relative humidity. Thermocouples are used to monitor the temperature and electronic circuitry is designed for simultaneous measurement of both temperature and temperature difference on the same single pen chart recorder. The system is used to monitor the daily variations of relative humidity inside the laboratories under different conditions.

Institute of Physics, Sri Lanka