Breckenridge, C.2023-02-062023-02-061996School Science Programme - 1996 (Weekend):Course Notes:p.19-25http://tri.nsf.ac.lk/themes/Mirage/1/IFS_SSP/SSP_COURSE_NOTES_1996/Separate/19.PDFhttps://dl-ifs.nsf.gov.lk/handle/1/2068Conference Paper