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Why does a kettle make noise before boiling?


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November 10, 2009 11:10PM

Because the water near heating element turns to water vapor. This vapor tries to rise up to the surface but as it meets colder water upwards it turns back into water. As the water/steam transition is not smooth (e.g. the volume changes rather rapidly during phase change), the constant transition between vapor and liquid states produces noise. As the water gets to +100C (boiling point), the vapor bubble will not turn back into liquid before reaching the surface thus making less noise.