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

1. Mar 6, 2004

### garytse86

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

2. Mar 6, 2004

### Integral

Staff Emeritus
What do you mean by "started heating"? You would need to know an inital temperature. Without that the question is pretty meaningless.

3. Mar 8, 2004

### garytse86

the information I posted above is all the information I have on the question.......

4. Mar 8, 2004

### Integral

Staff Emeritus
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

5. Mar 9, 2004

### Jules

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.