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In this lesson, we will discuss the following:. Heat Transfer. Conduction. Convection. Physics. Radiation. The Three Processes of Heat Transfer. Heat can be transferred from one substance to another through three processes: Conduction, Convection, and Radiation. Conduction. - PowerPoint PPT Presentation
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Heat Transfer
PhysicsIn this lesson, we will discuss the following:
Conduction
Convection
Radiation
The Three Processes of Heat Transfer
Heat can be transferred from one substance to another through three processes:
1. Conduction,2. Convection, and 3. Radiation
Conduction
Definition of Conduction
• Conduction is the transfer of thermal energy by the collision of charged particles.
• The particles involved in conduction are generally electrons, but protons in a liquid can also be involved in conduction.
Conduction Can Occur in Certain Phases
Conduction occurs primarily in solids, but it can also occur in liquids.
Good Conductors• Good conductors
are materials with lots of “free electrons.”
• Free electrons are just loosely-held outer electrons in atoms.
• All metals are good conductors (to varying extents).
Poor Conductors
• Poor conductors are just materials that do not have lots of free electrons.
• In fact, the atoms in poor conductors hold onto their electrons very tightly. It is very difficult to get a poor conductor to give up any electrons.
• Poor conductors are often called GOOD INSULATORS.• Dry air, wood, and Styrofoam are good insulators.
Substances containing lots of air are also good insulators. For instance, a down comforter has a lot of air trapped in it, and it is a good insulator.
Poor Conductors• Wood is a poor
conductor, and coal is made of wood.
• Because coal is made of wood, it is a poor conductor.
• Thus, the coals in the video do not conduct heat very quickly to the firewalkers’ feet.
Poor Conductors
The best insulator of all is a vacuum because a vacuum does not have
electrons or protons.
Convection
Definition of Convection Convection is
defined as the transfer of thermal energy through the bulk motion of particles (atoms and molecules).
Convection Can Occur in Certain Phases
• Convection can occur in anything that flows. Substances that flow are called FLUIDS.
Liquids and gases are both fluids.
Radiation
• Thermal energy can be transferred from one substance to another with ELECTROMAGNETIC RADIATION.
• Electromagnetic radiation is the same thing as LIGHT.
Radiation
• Everything with a temperature above absolute zero emits electromagnetic radiation.
• In other words, EVERYTHING EMITS ELECTROMAGNETIC RADIATION.
Radiation Can Move Through any Phase of Matter
• Electromagnetic radiation can travel through matter in any phase.
• Radiation can even travel through a vacuum!
• In fact, heat transfer in a vacuum can only occur with electromagnetic radiation.
The Electromagnetic Spectrum• Electromagnetic
radiation is the same thing as LIGHT.
• Only a small portion of the electromagnetic spectrum is visible to our human eyes.
The Electromagnetic Spectrum
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The Electromagnetic Spectrum The electromagnetic spectrum contains
all of the wavelengths of light, both visible and invisible to the human eye.
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The Electromagnetic Spectrum
• Look at the web page at the right.
• Notice: visible light is only a small sliver of the electromagnetic spectrum.
• The remaining wavelengths cannot be seen with the naked human eye.
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open.
The Electromagnetic Spectrum
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The Electromagnetic Spectrum
The Electromagnetic Spectrum
• The sun emits primarily in the visible portion of the electromagnetic spectrum.
• However, the sun does emit other wavelengths of light.
The Electromagnetic Spectrum
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The Electromagnetic Spectrum
•We perceive the infrared portion of the electromagnetic spectrum as heat.•We (humans) emit electromagnetic radiation in the infrared spectrum.•The earth also emits infrared radiation.
The Electromagnetic Spectrum
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the right does not
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The Electromagnetic Spectrum
Objects with dark surfaces absorb (and emit) radiation more easily than objects with light or shiny surfaces. Good at absorbing and
emitting radiation.
The Electromagnetic Spectrum
Objects with light or shiny surfaces absorb (and emit) radiation LESS easily than objects with dark surfaces. Bad at absorbing and
emitting radiation.
