Term
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Definition
| Heat is a form of energy. Input of heat to a system usually results in an increase of temperature - unless there is a change of state involved - then the energy is used to change state instead.
Output of heat from a system usually results in a decrease of temperature - unless there is a change of state involved - then the energy output is from the change state instead. |
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Term
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Definition
| Temperature is a measure of how hot or cold things are. It is an indication of how great the average kinetic energy of the particles in a substance is. The hotter the substance the faster the particles move and the more kinetic energy they have. |
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Term
| What unit is heat measured in? |
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Definition
| It is a form of energy so it is measured in joules (J). |
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Term
| What is temperature measured in? |
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Definition
| It is most commonly measured in degrees Celsius.
The Celsius and kelvin scales of temperature are used in science but there are others such as centigrade and fahrenheit which are common in other walks of life. |
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Term
| What temperature does pure ice melt at? |
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Definition
| Pure ice melts at 0oC or 273K |
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Term
| What temperature does pure water boil at? |
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Definition
| Pure water boils at 100oC or 373K |
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Term
| How can you measure the heat put into (or taken out of) a system? |
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Definition
| It can be measured with a joule-meter or a combination of instruments, the readings of which can be used to perform a calculation to establish the value. |
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Term
| How do you measure the temperature of a substance? |
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Definition
| It is measured with a thermometer. |
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Term
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Definition
| An instrument that measures temperature> There are many different kinds of thermometer, their range, sensitivity and constuction varies widely.
A thermometer can be made from anything which responds to temperature change.
You should know about the liquid in glass thermometer in detail. This uses expansion of liquids with temperature rise. |
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Term
| Which way does heat flow? |
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Definition
| Heat always flows from hot areas to cold areas - never say heat always rises!! It is hot FLUIDS that rise because of thier reduced density... |
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Term
| What affects how fast heat flows between two objects? |
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Definition
| The bigger the difference in temperature between the hot and cold object the faster the heat will move to the cold one.
The bigger the area of contact between the two objects the faster the heat transfer will happen.
Heat moves easily through good conductors of heat (such as metals) and very slowly through heat insulators (such as wood or plastic). |
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Term
| How does temperature differ in a conductor and insulator? |
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Definition
| The temperature of an object made of a good conductor of heat tends to be the same throughout the object but an insulator will be much hotter near the heat source than it is elsewhere. |
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Term
| What is a heat insulator? |
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Definition
| A material that does not allow heat energy to travel easily through it. |
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Term
| What is a heat conductor? |
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Definition
| A material that allows heat energy to flow easily through itself. |
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Term
| How does the colour and texture of an object affect how easily it gains or loses heat energy? |
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Definition
| Heat radiation is absorbed/emitted readily by dark, dull, rough surfaces and less easily by light, shiny, smooth surfaces. The temperature of dark, dull, rough surfaces will rise quickly if irradiated with infra red heat radiation and light, shiny, smooth surfaces will not respond as quickly. The hot surfaces will then give out the energy again at a similar rate to the way it rose in temperature.
A dull black object therefore takes heat from a source and radiates it out very efficiently, whereas a shiny white one is vey inefficient at doing this. |
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Term
| What are the three methods by which heat travels? |
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Definition
| There are three methods of heat transfer: conduction, convection and radiation |
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Term
| What happens to particles in conduction? |
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Definition
The particles pass the energy on to their neighbour only. A particle with more vibrational energy than its neighbour shares out its excess energy with that neighbour. Heat therefore travels along a solid sequentially.
[image][image] |
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Term
| What happens to particles in convection? |
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Definition
The less densely arranged particles rise within the fluid and take the heat energy with them.
As they move they share energy with any particles that have less than they do as they travel. In this way the heat energy moves throughout the fluid in a convection current.
[image] |
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Term
| What happens to particles in radiation transfer of heat? |
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Definition
The particles in the hot object give out a little packet of energy called a 'photon'. This is pure energy - infra red energy. The particle that gives out this IR radiation energy then vibrates slower.
The photon can travel through a vacuum. It goes in a straight line until it is absorbed by another particle - it makes that particle vibrate faster. |
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Term
| How does heat travel through a solid? |
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Definition
| By conduction - convection is not possible because the particles can't move around! |
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Term
| How does heat travel through a liquid? |
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Definition
| By convection mainly - some conduction does occur but that is a very slow process in a liquid. |
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Term
| How does heat travel through a gas? |
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Definition
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Term
| How does heat travel through a vacuum? |
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Definition
| By radiation - the only way heat can travel without particles interaction... and a vacuum has no particles in it. |
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