Heat And Temperature

Heat & Temprature By… Syeda Shafaq Batool & Rabia Tufail

Agenda    

Define Heat Heating & Cooling Heat Energy Identify the three ways heat can be transferred

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What is temperature Temperature Scales Common Temperature Comparisons Temperature conversions between the temperature scales

What is HEAT?

HEAT ENERGY

Form of energy and measured in JOULES • Particles move about more and take up more room if heated – this is why things expand if heated • It is also why substances change from: solids liquids gases when heated •

Heating and Cooling 

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If an object has become hotter, it means that it has gained heat energy. If an object cools down, it means it has lost energy Heat energy always moves from: HOT object

COOLER object

HEAT ENERGY •Energy

transfer Conduction Convection Radiation

Conduction 

Heat is transferred through a material by being passed from one particle to the next

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Occurs by the particles hitting each other and so energy is transferred.

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In this way heat in an object travels from: the HOT end

the cold end

Conduction cont… 

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Happens best in solids-particles very close together Conduction does not occur very quickly in liquids or gases

Conductors 

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Materials that conduct heat quickly are called conductors All metals are good conductors of heat Copper is a very good conductor of heat Pans for cooking are usually made with a copper or aluminium bottom and plastic handles

Insulators/poor conductors     

Materials that conduct heat slowly or poorly are called insulators Glass, wood, plastic and rubber are poor conductors (good insulators) Nearly all liquids including water are poor conductors (good insulators) Gases, including air are poor conductors,e.g., wool feels warm because it traps a lot of air A fridge has insulation material round it to keep it cold – reduces amount of heat conducted to inside from the warmer room

Convection 

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Takes place in material where particles can move around inside the material, i.e. liquid or gas Convection current rise up and the warmer molecules goes up to take their place, cooler molecules from the surface comes down Is a continuous process until the heat is being provided.

Convection Currents 

Hot liquids and gases expand and rise while the cooler liquid or gas falls 2. Goes across

3. Then down 1. Hot air rises

4. And across

Convection cont… 

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The sun can cause large convection currents - WINDS During daytime the land warms up more than the sea. The warm air rises over the land and cool air falls over the sea. So we feel a sea breeze.

Radiation 

Heat radiation is also known as

INFRA-RED RADIATION  

All objects that are hotter than their surroundings give out heat as infra-red radiation Heat transfer by radiation does not need particles to occur and is the only way energy can be transferred across empty space

What is temperature? Temperature is a degree of hotness or coldness that can be measured using a thermometer.  It's also a measure of how fast the atoms and molecules of a substance are moving.  Temperature is measured in degrees on the Fahrenheit, Celsius, and Kelvin scales. 

Temperature Scales 

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Three temperature scales are in common use in science and industry. The degree Celsius (°C) scale was devised by dividing the range of temperature between the freezing and boiling temperatures of pure water at standard atmospheric conditions (sea level pressure) into 100 equal parts.

Temperature Scales 

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The kelvin (K) temperature scale is an extension of the degree Celsius scale down to absolute zero, a hypothetical temperature characterized by a complete absence of heat energy. The degree Fahrenheit (°F) non-metric temperature scale was devised and evolved over time so that the freezing and boiling temperatures of water are whole numbers, but not round numbers as in the Celsius temperature scale.

Some baseline temperatures in the three temperature scales

Common Temperature Comparisons

Temperature conversions between the temperature scales kelvin / degree Celsius conversions  kelvin = degree Celsius + 273.15  degree Celsius = kelvin - 273.15 degree Fahrenheit / degree Celsius conversions  degree F = degree C x 1.8 + 32.  degree C = (degree F - 32.) / 1.8