Answer to Question #117945 in Other Physics for Arogundade Moses Temitope

Question #117945
An electric kettle has a 750W-240V heater and is used on a 200V mains. if the heat capacity of the kettle is 400J/K and the initial water temperature is 20°C, how long will it take to boil 500g of water, assuming the resistance of the heater is Unaltered on changing to the new mains.
Expert's answer

First, obtain the power of the kettle that is used at 200V-circuit:

@$R=\frac{V_1^2}{P_1}=\frac{V^2_2}{P_2},\\ \space\\ P_2=P_1\bigg(\frac{V_2^2}{V_1^2}\bigg)^2.@$

The amount of heat, on the one hand, is


and, on the other hand, it is the heat required to heat the water and kettle up:

@$Q=\Delta \tau(cm+C).\\ \space\\ t=\frac{V_1^2\Delta \tau(cm+C)}{V_2^2P_1}=384\text{ s}.\\ @$

It is equivalent to 6 minutes and 24 seconds.

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Arogundade Moses Temitope
26.05.20, 00:08

Ok following this illustration what is our "cm" and "C" denotes

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