P1.4/5/6/7 - Conduction & Convection, Radiation, Insulation and energy efficieny Flashcards Preview

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Flashcards in P1.4/5/6/7 - Conduction & Convection, Radiation, Insulation and energy efficieny Deck (23)
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What is conduction?

The transfer of energy through solid materials.


Particles in solids are always vibrating, even though they are fixed in position by forces between them. Why do particles vibrate MORE when they are hotter?

Particles vibrate MORE when they are hotter because they have more energy.


When heating one end of a metal object, how does the heat travel down to the other end?

When you heat one end of an object, the particles star vibrating MORE. The particles collide with other particles MORE and kinetic energy is transferred from one particle to its neighbor. Energy is conducted through the solid by particles colliding with each other.


What is a good thermal conductor?

A good thermal conductor is a material that conducts energy easily. Their particles are close together and in a regular pattern so vibrations are passed on easily. This is why radiators are made of metal. Metal is a good thermal conductor.


Some materials do not conduct heat very well and are called thermal insulators. What is a thermal insulator.

Materials such as wood and plastic are thermal insulators as they transfer energy/heat slowly. The particles are close together but the pattern is not as regular as it is in metal so this means that energy passes slowly from one particle to another.


Why are liquids and gases poor thermal conductors?

They are poor thermal conductors because their particles are not in an regular arrangement, so it is much more difficult for energy to be passed on through conduction. In gases the particles are very far apart which is why they are poor conductors. Double glazing works by having a layer of gas in between the two layers of glass.


How does energy transfer through free electrons work?

Metals have many free electrons in them that are free to move through the metal. This is also why they are good conductors of electricity. The free electrons gain more kinetic energy from collisions as the metal is heated. They transfer energy very quickly as they move through the metal.


What is convection?

Convection is when moving particles carry energy from one place to another.


What is a convection current?

The movement caused within a fluid by the tendency of hotter and therefore less dense material to rise, and colder, denser material to sink under the influence of gravity, which consequently results in transfer of heat.


Why can convection currents occur in liquids?

It can occur in liquids because cooler liquid is denser than heated liquid.


When you put your hands near or on a cup, energy is being transferred to your hand through conduction. This energy is being transferred by radiation. What is this radiation called?

Infrared radiation and is the transfer of energy by electromagnetic waves. ALL bodies emit and absorb infrared radiation.


If two objects are similar but one is hotter, the hotter one will emit ____ more infrared radiation.



Can you tell if something is emitting infrared radiation just by looking at it?

There are a couple of ways you can tell if something is emitting infrared radiation just by looking at it:
-It may be steaming
-It may emit light radiation (e.g red glow when smelting metal)


A dark matt surface is (i)____ at absorbing infrared radiation. A light coloured or shiny surface is (ii)___ at absorbing infrared radiation (it reflects radiation).

(i) good
(ii) bad


What is a medium?

The intervening substance through which physical forces are transmitted.


Why cant cavity wall insulation prevent heat loss by radiation?

Infrared radiation is an electromagnetic wave, like light. It can travel through a vacuum like light does. It does not need a medium to travel through. This is why cavity wall insulation cannot prevent heat loss through infrared radiation.


How may home owners try to reduce the cost of heating their house?

-They would try to insulate it better
-Reduce energy loss through conduction, convection and radiation.


What is pay-back time?

You can cut down on your energy bills by reducing the amount of energy you use. You can do this by making sure your house costs less to heat up. To do this you would invest in insulating methods. The amount of money you spend on your insulating methods divided by the amount of money saved on your bills every year is the pay back time. The method with the shortest pay back time is the most cost-effective.


What calculation can be used to work out payback time?

-Cost divided by savings per year.
E.g £250 divided by £100 savings per year = 2.5 years payback time


Which energy transfers in a TV are useful and which are not?

Light and sound energy transfers in a TV are useful whereas the heat energy from the TV is wasted.


What is a Sankey diagram used for?

A Sankey diagram is used to show the energy transfers made by an appliance. It shows the efficiency of the appliance, how much energy is wasted and how much is useful.


In a Sankey diagram the total energy input must always be the ____ as the total energy output.



What calculation can you use to work out how efficient an electrical appliance is?

efficiency = useful energy output / total energy input x 100

The unit used should be Joules or Kilojoules. The efficiency is given as a percentage.