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Heat Energy

Learn about heat transfer by conduction, convection, and radiation, specific heat, conductors vs. insulators, and energy vocabulary.

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Heat Energy

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  1. Heat Energy

  2. Thermal Energy Conversions I. Conduction - • Transfer of thermal energy by direct contact • Always from a solidhot object to a solidcold object • Takes place in solid, liquid or gases • Example:A metal spoon inside a saucepan gets hot while a saucepan is getting heated. If you were the chef in this picture and had to stir the contents for 20 minutes non-stop while on high heat – which type of spoon would you want to use?

  3. Conductors • Transfer heat easily • more tightly packed the particles, the better it is as a conductor • Most often Metals-metal spoon, metal pan, copper, iron, steel, silver

  4. Insulators ·does not allow heat to move easily through them ·wood, plastic, glass, fiberglass, air, Styrofoam • double pane windows (air between 2 panes of glass)

  5. Insulation R-value-rates insulation (higher number best) R-1 R-16 R-20

  6. Energy Vocabulary • absorbers-take in the energy • reflectors-reflect the energy • emitters-good absorbers that release energy later • dark and dull materials absorb • light and shiny materials reflect

  7. Thermal Energy Conversions Continued II. Convection - • Transfer of thermal energy in fluids – anything that flows • Always between liquids and gases • Example: hot air balloon, wind, ocean & air currents, home heating, all the soup in a pot becoming warm • warmer fluids (less dense) rise, buoyant convection • cooler fluids (more dense) sink • wearing sweater keeps the heat from being taken away from the body

  8. Thermal Energy Conversions Continued III. Radiation - • Transfer of thermal energy through waves. • Electromagnetic waves-light, ultraviolet rays, x-rays, infrared rays • Travels though gas and no air (vacuum) (outer space) • Colors reflect waves differently. • Black absorbs, White reflects • Example: sun’s energy, microwaves and radio waves infrared light bulbs, person warmed by a fire .

  9. Specific Heat What is specific heat? • the amount of energy needed to raise 1 gram of a substance 1°C in temperature • the property of a substance that tells us how much the temperature goes up when a given amount of heat is added • the lower the specific heat number the quicker it heats up or cools down • water has a high specific heat, metals have a low specific heat • specific heat of water is always 1.00cal/g·C° • If in joules it is 4.2 J/g·C˚

  10. Formula to calculate specific heat: Heat gained or lost = Mass X Change in Temperature X Specific Heat Q = (m)(ΔT)(Cp) Q = heat gained or lost (calories or joules or BTUs) m = mass (grams) ΔT = change in Temperature in °C (final temp – initial temp) Cp = Specific Heat (cal/g°C) or (J/g·C˚)

  11. Formula Substitute Answer Calculating Specific Heat If the specific heat of copper (Cu) is 0.09cal/g°C, how much heat is needed to raise the temperature of 5 grams of copper by 10°C? Step 1 Read the problem. Draw a picture. Step 3 Set up the formula. Step 4 Substitute the numbers. Solve. Box Answer with units. Step 2 Write down what you know. What are you trying to find? Cp= 0.09cal/g°C M = 5g Q = (m)(ΔT)(Cp) Q = (5g)(10°C)(0.09cal/g°C) Q =4.5cal ΔT = 10°C 4.5cal Q =

  12. Do Problems 1 & 2 in Your Notes.

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