Objectives:

• To understand what the term insulation means and how it links to conduction
• To be able to understand why some materials are better at insulating than others.
• To be able to explain how you would carry out an experiment to determine the effectiveness of an insulator.

There are two types of insulation:

• Thermal insulation – whereby a substance restricts heat flow through itself
• Electrical insulation – whereby  substance restricts electrical current from flowing through it.

This section discusses thermal insulation but it is important to note that objects that are good electrical insulators are also good thermal insulators, the reason for this is that they have very few delocalised electrons in them. Objects that are not very good insulators are known as conductors, they conduct well for the opposite reason – they have lots of delocalised electrons.

Insulation and conduction are two words used to describe opposite effects – a bit like radio waves and gamma rays, these are both types of electromagnetic waves but have different names due to being at opposite ends of the spectrum.

The following image shows insulation on the left and conduction on the right, there are a number of materials that can be arranged on this arrow, can you arrange them correctly before looking at the answers below?Hopefully you can appreciate that the materials that conduct well (because they have a large number of delocalised electrons) are metals (this is why they are used to conduct electricity) and so should all be on the right hand side of this arrow. Those that conduct less well and are therefore insulate better are substance like wood. Air is also a good insulator but this is because it is a gas and so the particles are far apart – the further apart the particles are the harder it is for electrons to flow between them (and hence be ‘delocalised’).

The answer to the ‘insulates and conducts’ image above is as follows;Materials used for Insulation have improved over the past 50 years or so tremendously. What items in your home do you think prevent heat from escaping, thereby keep you warm and cosy in the winter months?The image above shows areas of the house where heat can be lost. So these would be the regions that need some form of insulation.

Insulating your home

The following is a list of examples that can be used to keep the heat in. You could always just turn the heating up… but the problem with this is it is damaging for the environment and costs a lot of money!

• Double Glazing – two panes of glass with trapped air (or argon gas) in the middle. The first pane may conduct heat through but then air (which is a good insulator) prevents heat from getting through to the next pain.
• Roof insulation – usually made with fibre glass and appears like a type of wool. Because it is made of tiny strands of glass it reflects the heat back and prevents it from getting through. Because heat ‘rises’ the roof is imperative to get insulated. If you live in a flat, then you should ensure that the flat above your has underfloor insulation.
• Underfloor insulation – Heat can conduct through the carpet, so insulation in the floor can allow heat to stay in the room rather than go below it.
• Draught excluders – Most doors have gaps underneath them, some may be small but other large. This can allow lots of heat under and able to leave your house (especially if it is an external door), so a draught excluder can be placed down to temporarily block the gap.
• Cavity wall insulation – This is a layer of insulation between your external wall and the room inside. Usually, there are two layers of bricks on the outside of a house, between the bricks is a layer of insulation. It is called cavity wall insulation because it fills the void. This void is filled with materials that trap air and as a result minimise heat escaping through the walls.

Underfloor heating is not a form of insulation – insulation prevent heat from getting through… it does not supply new heat.

There are three types of heat transfer that all insulating objects and buildings try to prevent, these are conduction, convection and radiation.

Conduction – this is a process in which, when the first particle heats up and gains energy it will collide with neighbouring atoms making them vibrate which will in turn cause their neighbouring atoms to vibrate and heat up. Conduction is also due to free electrons within a material. The more free electrons, the quicker these electrons can travel through a material colliding with local atoms transferring the energy.

Convection – Take two regions of air (isolat
ed from all other things) filling a 1 metre cubed volume. If one were heated, all the particles begin the vibrate and move faster, this causes more collisions and expands the gas – this results in the volume that is being heated to expand, thus increasing the volume. The number of particles will have remained the same.
Therefore $m = text{same}$ and $V = text{larger}$.
Using the equation for density studied earlier in this topic $\rho = \frac{m}{V}$ we can see that the density must decrease because we are dividing by a larger number:
$\frac{m_{same}}{V_{larger}} = \rho_{smaller}$
This means heated substances rise because more density substances fall.
Convection is the cause of winds all around Earth and is also linked to specific heat capacity.

Radiation  is the transfer of heat through light. All waves in the electromagnetic spectrum are forms of light and travel as waves. These waves transfer energy from one location to another (i.e. from the sun to Earth), fortunately they do not need a medium (a substance) to travel in. I
f they did require a medium we would seize to exist on Earth due to us being surrounded by empty space known as a vacuum.