- Hey guys,
in this video we are going to be look at
some specific heat capacity.
Now there's quiet a lot going on in this practical.
There's lots and lots of different questions
the examiner is going to ask you.
So there's lots and lots of different ways
maths can fit into this.
So to help you really really
prepare for this
I've written you a load and load of questions.
You can get the combines science questions
or you can get the separate science questions.
(upbeat music)
Back in the lab again.
He is all set up for specific heat capacity.
We have our blocks
we have our thermometer.
We've got aluminum set up at the moment
And we have iron and copper.
We can take our start reading on the block
and in the hole in there
we need some water.
We can see this is connected up to
a power unit.
So we're going have a power going in
through here and
we have this connected up to a multi meter.
But you might have it come through to
a volt meter and meter, even a dual meter.
Here we have a diagram of the practical.
We have our block, a thermometer, and you need a
tiny bit of water in here.
Just to get rid of this air gap so that the energy
in here can be transferred easily and can be read by
a thermometer.
This is our heating element and it's going to be
connected up to power.
What is actually connected up to here will vary
depending on what equipment your school has access to.
It can be connected up to a joule meter where you can
read the joules directly.
Or like I've used, it can be connected up to a volt meter
and ammeter.
We have to do a tiny bit of maths.
So here is my complete circuit.
You saw on the video I was using 12 volts as my
power input
the actual reading on the multi meter was 9.8 volts and
then the ammeter reading was 2.8.
I've drawn the circuit here correctly not including a
multi meter, so we have our ammeter in series
and our volt meter in parallel across the component
that we're measuring the potential difference across.
It is highly unlikely that your measured voltage
across the component
will be the same as what your power pack is set to.
There are a lot of equations in this.
We have energy.
Which is measure in joules.
Equal to mass, measured in kilograms.
Times specific heat capacity.
Units for this one are slightly tricky.
They are joules per kilogram degree C
and then temperature change
this is temperature and this means change
so this is temperature change.
Temperature change is measured in degrees C.
Now if you have joule meter you can measure your
energy directly but we don't.
So we're going to be using energy in joules is
equal to power, in watts
times time in seconds.
To find the power, which is measured in watts.
We are going to use our readings from the ammeter
for current.
And our readings for potential difference
from the volt meter.
I know there are a lot of equations on this page
and maybe this looks bit more complicated than it did
in school.
But I'm going to break this down for you.
We saw from our experiment that we have a
current of 2.8 amps,
and we had a potential difference of 9.8 volts.
Giving us power in to the system of 27.44 watts.
Now we've used uh this equation here to work out
power, we can use this equation over here to work out
the energy.
So that is simply the time, which is down this one
times the uh power, which is this value here.
So 60 times 27.44, 120 times 27.44, 180 times 27.44,
240 times 27.44.
And we're going to be using these values to plot our graph
We know from our experiment what the
starting temperature was.
We can just read that off.
And then what we are going to be adding in this
column down here is the temperature.
And we're going to be taking that temperature
reading every minute.
This is for the aluminum block.
You might have plated your results are a class
or you might have done all of the blocks.
Now we finished the experiment
we're going to plot the graph.
And on the x axis we are going to be plotting the energy
or the work done, they're the same value
and I'm going to plot them in kilojoules
so it's simply just the first value
and then up the y axis we're going to be plotting
temperature.
Changing that in there.
Now you may have just plotted time along this
axis. That's absolutely fine, just means you'll
have to do a bit more maths later on.
Making a fatal mistake of not putting things in the right
place.
Once you've got your points in you can draw your line
of best fit.
And then we can find our gradient.
Now finding your gradient is always going to be done
by taking the up value and diving it by the across value.
Draw the biggest triangle that you can.
However, it is kind of helpful if you draw the triangle
so it lines up with known values.
It just makes things a bit easier for you.
On construction lines are always a really good idea
so the examiner can see clearly that you know what is
going on.
And then showing all of your working.
So you're showing the difference.
That 37.5 minus 25.
Clearly showing the examiner what they are looking for.
Showing them that you know what you are doing.
Right, that page was getting a bit busy so we're moving
on to a clean page.
So we can get our actual value for the gradient as .00129
now the specific heat capacity can be found by one
divided by the gradient.
So specific heat capacity for my experiment came out as
773 joules per kilogram degree C.
Now we haven't used this equation over here,
so that's what we're going to do now.
Rearrange the equation to find specific heat capacity.
And then I just like to write all the values down
so I know what we're looking for.
Mass is one because it's a one kilogram block.
Energy, that is the time energy at ten minutes.
And then the temperature change at ten minutes.
Popping those numbers into the equation.
And by calculations, we get a value of
784 joules per kilogram degree C.
Different, but actually pretty close to my
experimental value.
Now the actual value for this is
900 joules per kilogram degree C.
You would never expect to get the actual value in a
experiment but you need to think about why it is
different.
For example, could adding insulation around the block
so that all the energy from the heating element
was transferred to the block and then to the
thermometer and not so that the block ending up heating
the outside air.
How much of a difference would that have made?
For every single practical, you need to know the
independent variables, the dependent variables.
So here we were measuring temperature change,
you could change the block that you were using,
the control variables- what did we keep the same.
And a risk assessment.
This one involved heavy blocks and electricity.
The sources of error and how to prevent them.
For example, energy loss to the surrounding air, we
could insulate it.
Any alternatives. For example, we were using a
thermometer whereas a data logger would be more accurate.
Lots of equations in there that need rearranging and
some tricky units you need to remember.
A large number of calculations which I'm afraid you
just need to practice for this,
especially finding the gradient.
A step by step method, which I've gone through
any graphs that come up.
You may find a graph that has a bit of a lag period
at the end.
That's just while the heating element warms up.
And you need to be able to label any diagrams of
equipment and if you've done, if you've used a
joule meter in class, do not be surprised or do not
be thrown if a volt meter or ammeter come up in class
or vice versa.
(upbeat music)