Temperature change of water flowing through heater
an immersion heater supplies 8.5kJ every second, water flows in at a rate of 0.12kg/s, and the heating chamber holds 0.41kg of water.
the question is: "Assumingall the energy is transferred to the water,calculate the rise in temperature of the waters it flows through the heater"
so I use Q=mct, but I'm unsure what to use for the mass. the energy proceed by the heater is going to "spread out" across the 0.41kg in the heater, so I think I should use 0.41kg. however the question does say "flows" so that makes me think I should use 0.12. The markscheme uses 0.12 but I'd like to know why it's not 0.41?
(the question is from A2 AQA unit 5, question 1 June 2012 btw)
the question is: "Assumingall the energy is transferred to the water,calculate the rise in temperature of the waters it flows through the heater"
so I use Q=mct, but I'm unsure what to use for the mass. the energy proceed by the heater is going to "spread out" across the 0.41kg in the heater, so I think I should use 0.41kg. however the question does say "flows" so that makes me think I should use 0.12. The markscheme uses 0.12 but I'd like to know why it's not 0.41?
(the question is from A2 AQA unit 5, question 1 June 2012 btw)
Original post by jon889
an immersion heater supplies 8.5kJ every second, water flows in at a rate of 0.12kg/s, and the heating chamber holds 0.41kg of water.
the question is: "Assumingall the energy is transferred to the water,calculate the rise in temperature of the waters it flows through the heater"
so I use Q=mct, but I'm unsure what to use for the mass. the energy proceed by the heater is going to "spread out" across the 0.41kg in the heater, so I think I should use 0.41kg. however the question does say "flows" so that makes me think I should use 0.12. The markscheme uses 0.12 but I'd like to know why it's not 0.41?
(the question is from A2 AQA unit 5, question 1 June 2012 btw)
the question is: "Assumingall the energy is transferred to the water,calculate the rise in temperature of the waters it flows through the heater"
so I use Q=mct, but I'm unsure what to use for the mass. the energy proceed by the heater is going to "spread out" across the 0.41kg in the heater, so I think I should use 0.41kg. however the question does say "flows" so that makes me think I should use 0.12. The markscheme uses 0.12 but I'd like to know why it's not 0.41?
(the question is from A2 AQA unit 5, question 1 June 2012 btw)
Because 0.12Kg of cool water flows in every second, and 0.12Kg of heated water must flow out every second. Irrespective of how much is already in the tank, only 0.12Kg needs to be heated every second.
(edited 10 years ago)
Original post by uberteknik
Because 0.12Kg of cool water flows in every second, and 0.12Kg of heated water must flow out every second. Irrespective of how much is already in the tank, only 0.12Kg needs to be heated every second.
but just because the 0.29kg of water is "old" doesn't mean it's not heated by that energy?
it doesn't selectively heat the newest 0.12kg of water and just leave the "old" water at the temperature it was at after it entered and was heated for one second.
Original post by jon889
but just because the 0.29kg of water is "old" doesn't mean it's not heated by that energy?
it doesn't selectively heat the newest 0.12kg of water and just leave the "old" water at the temperature it was at after it entered and was heated for one second.
it doesn't selectively heat the newest 0.12kg of water and just leave the "old" water at the temperature it was at after it entered and was heated for one second.
The heater does not select which water molecule to heat.
Heat energy only flows from hot to cold so the incoming cold water will immediately start to heat as soon as it encounters a heat source. i.e. other water molecules in the chamber that are already being heated.
The flow of water through the heater must eventually carry away all the energy input to it. Before that point is reached, the net outflow of energy is less than the energy input by the heater and so excess energy is stored as a rise in temperature.
The temperature stabilises when the exchange of energy imparted from the heater to the water reaches an equilibrium with the outgoing heat energy carried away by the outflow of water.
(edited 10 years ago)
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