Conduction (GCSE Physics)

Uploaded by freeeschool on 04.09.2012

GCSE Physics - Conduction
Hello! Welcome. Today, we are looking at heat transfer; how heat energy can be transferred
from one place to another.
There are three methods and three videos for this. The one we are looking at today is called
Conduction. Let’s have a look and see how it works.
Here, I’ve got some particles, in this example, a metal. So if you imagine, I’ve got a metal
rod, a badly-drawn metal rod, and I’ve taken one small part of it and expanded it so you
can see what’s happening with the atoms. That’s what I’m trying to represent there.
Ignore the colors for the moment; I’ll explain that in a minute.
Now, we’ve got the atoms in the metal rod and imagine this point here, we are heating.
What tends to happen with materials such as metals, or in fact, metals is that once you
heat a particular part of the metal, that heat can be transferred along the piece of
metal. You can see here that while I’m heating in this corner, you can see the heat, by the
colors, is spreading along the piece of metal.
Now, the way this works happens for a couple of reasons. The first one is when you heat
this particular corner, what you do is you transfer heat energy from your heat source:
a burner or whatever it is, to the atoms of the metal. What happens to this atom is that
it starts to vibrate and the more heat energy you give it, the more vigorously it vibrates.
You can imagine then and as you can see from what we are doing here that at some point,
it starts to vibrate enough that it bangs or knocks into its neighbor. Once it knocks
into its neighbor in that way, you can see that neighbor will start vibrating quite vigorously
as well and its neighbor will start to vibrate and so on and heat energy, in that way, will
be transferred or passed along the piece of metal.
There is one other reason why metals are quite good at conducting heat and that is because
they have, all around the atoms, electrons that are free to move. We call these “delocalized”
electrons. That means that they are free to move and they also contribute because they
are able to move and they can also transfer heat energy along the metal by conduction,
so they contribute as well. That’s generally how conduction works and any material that’s
good at transferring heat in this way is a good conductor. If a material is bad at conducting
heat or not able to transfer heat in this way very well, we call it an insulator.
Some materials are good insulators and the reason for that is as follows. Here I have
a piece of wood which is a very good insulator. In other words, it is poor conductor. The
reason for that is it doesn’t have what we call delocalized electrons. It doesn’t
have electrons that are free to move as in metals, but also, if we look at the arrangement
of the atoms, they are not aligned very neatly in rows and columns as they were in metals.
Once they vibrate, it is harder for them to pass on that heat energy to their neighbors
because they are not aligned as nicely and as neatly. As I said, no free electrons.
Something like air is also a very good insulator or a poor conductor. If we are talking about
air that is still, that is air that is not being blown around or wind but air that is
fairly still, you can see that there is a big distance between the air particles. Therefore,
if you are heating a particular area, it is hard for them to bang into their neighbors
and pass on heat through conduction. They can actually pass on heat energy in a different
way through convection, which is slightly different, but still air or air that is not
moving is a very good insulator.
It is probably worth a good note of this because this idea is used for insulating various things.
It is used in winter coats that have layers of feather inside the material that stop the
air from moving around and making a good insulator. Lots of animals take advance of this. For
example, polar bears have a thick layer of fur but they also have hollow fur which gives
it a layer of still air over their body surface which helps to insulate their bodies.
That’s an overall description of how conduction works and you should be able to describe how
atoms vibrate, passing down energy to their neighbor, what makes metals good conductors
and what makes other materials poor conductor.
[end of audio – 05:09] GCSE Physics - Conduction