I have got a problem here:I was given this:A 125W heater and

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Discussion Overview

The discussion revolves around a problem involving a 125W heater and a thermometer in 0.6kg of oil, focusing on determining the time at which heating started based on temperature data collected over time. The scope includes conceptual understanding and mathematical reasoning related to energy balance and temperature change.

Discussion Character

  • Debate/contested
  • Mathematical reasoning
  • Conceptual clarification

Main Points Raised

  • Gary questions how to find the time at which heating started, suggesting it might be the x value when y = 0, even if that results in a negative time.
  • One participant argues that without an initial temperature, the question lacks meaning, implying that the starting point of heating is ambiguous.
  • Another participant interprets the problem as indicating that heating started at t=0, suggesting this is the only reasonable interpretation.
  • A different viewpoint expresses skepticism about the sufficiency of the provided information, proposing that the question likely contains a typo regarding the starting temperature.
  • This participant also presents a mathematical approach using an energy balance equation, indicating that if heating starts at t=0, the temperature function can be derived from the data, and notes that negative time values are relative.

Areas of Agreement / Disagreement

Participants express disagreement regarding the interpretation of when heating starts and the sufficiency of the information provided. There is no consensus on how to approach the problem or what assumptions can be made.

Contextual Notes

Limitations include the lack of an initial temperature, which affects the interpretation of the data and the assumptions about when heating begins. The discussion also highlights the ambiguity surrounding the definition of time zero in this context.

garytse86
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I have got a problem here:

I was given this:


A 125W heater and a thermometer are immersed in 0.6kg of oil in a vessel of negligible heat capacity. The following results were obtained.

Temperature (K) 294 302 313 324 334
Time (minutes) 2 4 6 8 10

How would you find the time at which heating started?

would it be the x value when y = 0, but x (time) would be negative.

Can someone help? Thank you.

Gary
 
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What do you mean by "started heating"? You would need to know an inital temperature. Without that the question is pretty meaningless.
 
the information I posted above is all the information I have on the question...
 
The only interpetation of that problem that makes any sense is that the heaters were turned on at t=0. Thus heating started at t=0
 
I don't believe there is enough info given.
Most likely it is a typo and the requirement is actually the starting temperature.
In this case a way to do it would be:

An energy balance on the oil,

m.Cp.[T - T0] = q.t

(assuming heating starts at t=0)

So,

T(t) = (q/m/Cp)t + T0

Take the data & plot. Should be straight line of intercept T0.

p.s. There's nothing wrong with time being negative, it's all relative to where zero is defined.
However a temperature of zero kelvin is highly unlikely, i.e. your oil would probably be a frozen rock.
 

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