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INVESTIGATING HEAT ENERGY

INVESTIGATING HEAT ENERGY . 7.1 Heat and temperature. Heat is a form of energy that is measured in joules(J). Heat and temperature are not the same. Temperature is a measure of how hot or cold something is. It is measured in degrees Celcius ( 0 C) using a thermometer. Heat and temperature.

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INVESTIGATING HEAT ENERGY

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  1. INVESTIGATING HEAT ENERGY

  2. 7.1 Heat and temperature • Heat is a form of energy that is measured in joules(J). • Heat and temperature are not the same. • Temperature is a measure of how hot or cold something is. • It is measured in degrees Celcius (0C) using a thermometer.

  3. Heat and temperature • For example, each spark in a sparkler is a tiny piece of white hot metal, and its temperature may be as high as 8000C. • Boiling water is only 1000C. • However, if a spark falls on your hand you don’t even feel it. • This is because each spark contains only a small amount of heat energy.

  4. Heat and particle theory • When you heat an object, the particles in it move more rapidly and have more energy. • This is why the temperature is higher. • When the particles lose energy and move more slowly, the temperature is lower. • For example, slushies and cups of coffee.

  5. 7.2 Heat transfer • Heat energy can be transferred in three different ways: • Conduction • Convection • Radiation

  6. Heat transfer (conduction) • Conduction – this is how heat energy is transferred through solids. • For example, when a hot metal rod comes in contact with a hot flame, it becomes hot quickly. The heat is transferred along the rod by the process of conduction. • Metals are good conductors • Plastics and glass are poor conductors

  7. Heat transfer - Convection • Convection – this is how heat energy is transferred in liquids and gases. • For example, convection currents occur when water particles at the bottom of a beaker are heated, The hotter (less dense) water near the bottom rises, and the cooler water becomes more dense and sinks. • Can you think of other types of convection currents?

  8. Convection currents in the atmosphere drive weather patterns Convection currents in a radiator - warm air rises and cool air sinks Convection currents in the mantle drive tectonic plate movement

  9. Heat transfer - Radiation • Radiation – this is how heat energy is transferred from the sun to the earth. • For example, when the sun heats the earth, heat is transferred by the process of radiation. • Can you think of other situations in which radiation might occur?

  10. Medical Radiation Xrays Mobile phone radiation Cosmic radiation Heat radiation

  11. Absorbing and emitting Radiation • Dark coloured surfaces are better absorbers of radiation than light-coloured surfaces. • This is because light-coloured surfaces reflect more radiation. Roof insulation has light-coloured surfaces to reflect more radiation. Solar panels have dark shiny surfaces to absorb more radiation.

  12. Absorbing and emitting Radiation • All objects emit infrared radiation if they are at a higher temperature than their surroundings. • Rough surfaces also radiate heat more effectively due to their greater surface area. • Many animals will also sunbath to absorb radiation.

  13. Controlling heat transfer • An object that is warmer than its surroundings will lose heat until it is the same temperature as its surroundings. • Similarly, an object that is cooler than its surroundings will gain heat from its surroundings. • Insulators are used to control the transfer of heat. • For example, Eskys and flasks

  14. 7.3 Heat in everyday life • Turn to page 168 in your text book • Complete 2 activities from the following list: • Firewalking • How does a thermos work? • Which is the coolest colour to wear? • Does white coffee cool faster than black coffee? • Why use a lid? • Designing a house

  15. Energy: Review questions • Complete the following questions • Explain the difference between heat and temperature. Give the units that each is measured in • Why do you not get burned by sparklers, even though they have a higher temperature than boiling water? • Give the three different ways in which heat can be transferred. Give an example of each. • Why are plastics used to make handles for saucepans, kettles and frying pans? • Why is radiation of heat important? • Can you think of why absorbing panels of solar water heaters are painted black? • Name three ways in which insulators are used to control the transfer of heat.

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