Determining the specific heat capacity of water

[VegemiteJuice]

Homework Statement

Hi,
I have an assignment to determine the specific heat capacity of water using a calorimeter, voltmeter and ammeter, where we connected the calorimeter to a 10V power pack and measured the temp of the water and the readings on the voltmeter and ammeter every minute. I ended up having a huge random error for the voltmeter and ammeter (3.01%) - any idea why this is?
Also what should I talk about in my discussion?

Homework Equations

To calculate the specific heat capacity I used
PΔt = mc(water)ΔT + mc(calorimeter)ΔT
and I got a value of 3.95 +- 3.45% J g-1 K-1

 

[CWatters]

What do you mean by a "huge random error for the voltmeter and ammeter"? Were the readings fluctuating up and down? Changed gradually over time?

 

[BvU]

Hi Juice,

So you have three series of T, I and V as a function of time. It would be logical to plot them as a function of time to see if the errors are really random, or that there is more going on.

 

[VegemiteJuice]

What do you mean by a "huge random error for the voltmeter and ammeter"? Were the readings fluctuating up and down? Changed gradually over time?

We wrote down the measurements displayed on the ammeter and voltmeter every minute, until the water had increased by over 20K (it took 5 minutes). The readings on each fluctuated every time, and the random errors were 0.11A and 0.1V, which ended up being quite a large % error.

 

[BvU]

How do you know they were errors ?

 

[VegemiteJuice]

Hi Juice,

So you have three series of T, I and V as a function of time. It would be logical to plot them as a function of time to see if the errors are really random, or that there is more going on.

Alright, I'll try that.
Thank you BvU!

 

[lychette]

did you stir the water during the experiment?

 

[CWatters]

+1 to the questions above.

Also..

How many digits could the meters display? 10.1V is three significant digits. Could it display 10.05V or is 10.1V the nearest it can get?
What was a typical current? Something like 3.11A is also three significant digits.