Hi iSean,
*Before we continue, do take note that Cambridge A level will
not explicitly test you on this experiment on how you should
approach doing it, although you should know it. To do well, you
need to focus on the things that they test more frequently on.*
The input and output temperatures are always adjusted to be the
same to ensure that any heat loss to surroundings is kept constant.
As such, we are able to let it be a constant which can be
deducted.
The formula involved is Pt = mc Δθ +
H, where H refers to the heat loss to surroundings.
Let's go into the details of the experiment.
Δθ and t are variables to be kept
constant so that H becomes constant, because rate of H depends on
the temperature difference between the water and the
surroundings.
c is a constant which you need to measure.
m is the mass of the amount of water collected.
For the experiment, you need
to vary P by whatever means you have learned in Circuits (i.e.
varying resistances, current, p.d., or even e.m.f.), and adjusting
the flow rate to ensure Δθ
and t are constant
to ensure a constant H.
Because the flow rate is varied, different values of P will give
different values of m, the mass of water collected.
So by doing the experiment with two different values of P, you
will get
P1 t = m1 c Δθ +
H -------- (1)
P2 t = m2
c Δθ +
H -------- (2)
Because you have kept Δθ
and t constant, H
will be a constant. Hence, we are able to take (2) minus (1) and
eliminate H.
From there, the value of c can be determined because every other
variable is known (maths concept of simultaneous equations).
I just like to analyse the procedure on how to do the experiment
itself, to get the bigger picture. :)
Well i think I finally understand the full story now. Thanks
Eagle.
