The pressure unit is Pascal (sign Pa) or Newton per square meter (N / m2). In addition to Pascal, a pressure measurement unit can be used bar (1 bar = 105 Pa). The old pressure units are: technical atmosphere, the symbol at (1 at = 98 066.5 Pa); standard, normal or physical atmosphere, atm (1 atm = 101 325 Pa); millimetres of mercury, the symbol mmHg, or torr (1 mmHg = 1 torr = 133,322 Pa); millimeter of water, symbol mmH2O (1 mmH2O = 9.806 65 Pa).
J.J. Thomson’s experiments with cathode ray tubes showed that all atoms contain tiny negatively charged subatomic particles or electrons. Thomson proposed the plum pudding model of the atom, which had negatively-charged electrons embedded within a positively-charged “soup.”
