thermodynamics 1st report - 29 slides

8/6/2019 Thermodynamics 1st Report - 29 Slides

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Basic Forms of Energy cont¶d «

y Thermal or Heat Energy:

Consider a hot cup of coffee. The coffee is said topossess "thermal energy", or "heat energy," which isreally the collective, microscopic, kinetic, and

potential energy of the molecules in the coffee.



Basic Forms of Energy cont¶d

y Electrical Energy All matter is made up of atoms, and atoms are made up

of smaller particles, called protons, neutrons, andelectrons. Electrons orbit around the center, or nucleus,

of atoms, just like the moon orbits the earth. Thenucleus is made up of neutrons and protons.

Material, like metals, have certain electrons that areonly loosely attached to their atoms. They can easily bemade to move from one atom to another if an electricfield is applied to them. When those electrons move

among the atoms of matter, a current of electricity iscreated.




´Electromagnetic Energy (light):« Consider the energy transmitted to the Earth from

the Sun by light (or by any source of light). Light,which is also called "electro-magnetic radiation".

Why the fancy term? Because light really can bethought of as oscillating, coupled electric andmagnetic fields that travel freely through space(without there having to be charged particles ofsome kind around).

« It turns out that light may also be thought of as

little packets of energy called photons (that is, asparticles, instead of waves). The word "photon"derives from the word "photo", which means"light".




y Nuclear Energy:

The Sun, nuclear reactors, and the interior of the Earth,

all have "nuclear reactions" as the source of their energy,

that is, reactions that involve changes in the structure of the

nuclei of atoms.



R EV IE W

y Thermal or Heat Energy: Kinetic energy due to disordered motions of microscopic as molecules or atoms.

y Chemical Energy: Energy held in the covalent bonds between atoms in amolecule.

y Electrical Energy: Energy made available by the flow of electric charge through

y ElectrochemicalEnergy: A combination of electrical and chemical energy whereenergy is stored in a chemical way.

y Sound Energy: Energy transmitted by pressure waves through air or othermaterial.

y ElectromagneticEnergy: The energy that travels in waves, such as ultra-violetradiation. It can be thought of as combination of electric and magnetic energy.

y Nuclear Energy: Energy that is created by splitting atoms of radioactive materialsuch as uranium.



How is energy transported from place to

place and transferred between objects?

y The most obvious and trivial way in which

energy is tr ansported is when an object thatpossesses energy simply moves from one placeto another.

y For example, a baseball flying through

the air is a simple form of energytransport.



Energy Transfer continued

y Kinetic energy can also be tr ansf erred from one

object to another when objects collide. This is also

pretty trivial, except that we also know that the

total energy, including any heat or other forms ofenergy generated during the collision, is conserved

in this process, regardless of the relative sizes,

shapes, and materials of the objects.



HEA T

y There are three important ways that heatenergy can be transported or transferred,called conduction, convection, and radiation.

y The first two refer to transfer of the thermalenergy, whereas the last is really a conversionof energy to a different form, (photons of light) and the subsequent travel (transport) of those photons.



N A TUR E OF HEA T

Heat is a transfer of thermal energy from anobject at a higher temperature to an object at alower temperature.

Heat is transferred by conduction, convection, andradiation.

A conductor transfers heat well whereas an insulator doesnot.

The amount of heat necessary to raise a given mass of asubstance by a specific unit of temperature is called thespecific heat.



K EY TERMS

Conduction ± The transfer of heat betweenparticles within a substance.

Convection ± The transfer of heat by the

movement of currents within a fluid.

Convection current ± The transfer of heat by the movement of currents within a fluid.

Radiation ± The transfer of energy by electromagnetic waves.



K EY TERMS

Conductor ± The material that easily transfers heat between its particles.

Insulator ± A

material that does noteasily transfer heat between its particles.

Specific heat ± The amount of heatrequired to raise the temperature of onekilogram of a substance by one gramKelvin.



Conduction

� The "diffusion" of thermal energy (heat) through asubstance, which occurs because hotter molecules

(those that are vibrating, rotating, or traveling

faster), interact with colder molecules, and in the

process transfer some of their energy.

� Metals are excellent conductors of heat energy,whereas things like wood or plastics are not goodconductors of heat. Those that are not so good

conductors are called insulators.



Convection

y The transfer of heat energy by the movement of a

substance, such as a heated gas or liquid from one

place to another.

y For example, hot air rising to the ceiling is anexample of convection (in this case called a

convection current).



Radiation

y In the context of heat transfer, however, theterm "radiation" refers just to light (electro-magnetic waves), and in particular, to thesurprising fact that all objects, even those that

are in equilibrium (at equal temperature) withtheir surroundings, continuously emit, orradiate electromagnetic waves (that is, lightwaves) into their surroundings.

y The source of this radiation is the thermal

energy of the materials, that is, the movementof the object's molecules.



yConduction²scorching yourhand when you grab the handle of a

hot potyConv ection² boiling water

yR

adiatio

n²standing in front of your fireplace



First Law of Thermodynamics

y Energy can be changed from one form to another, but it cannot be created or destroyed.

y The total amount of energy and matter in the

Universe remains constant, merely changing fromone form to another.

y The First Law of Thermodynamics (Conservation)states that energy is always conserved, it cannot

be created or destroyed.



Second Law of Thermodynamics

yStatement: ³ I n all energy exchanges,if no energy enters or leaves thesystem, the potential energy of the

state will always be less than that of the initial state.³



Third Law of Thermodynamics

y A ll processes cease as temperature

approaches absolute zero. This is thetemperature at which molecules ceasemovement, cease producing kinetic

energy. In other words, there is noenergy.

thermodynamics 1st report - 29 slides

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