energy transfer thermal energy & em spectrum unit 9 section 1 notes

Energy Transfer

THERMAL ENERGY & EM SPECTRUM UNIT 9

SECTION 1 NOTES

All forms of matter, whether a solid, liquid, or gas, are composed of atoms or molecules in constant motion. Because of this constant motion, all atoms have kinetic energy in the form of thermal (heat) energy.

Whenever a substance is heated, the atoms move faster and faster. When a substance is cooled, the atoms move slower and slower.

THERMAL ENERGYTHERMAL ENERGY

When the motion of particles (kinetic energy) increases, so does the temperature.

When the motion of particles decreases, so does the temperature.

The "average motion" of the atoms that we sense is what we call temperature.


Temperature and heat ARE NOT technically the same thing. Temperature is the average motion of atoms and molecules. Heat is the energy that flows due to temperature differences. Heat is always Heat is always transferred fromtransferred from warmer to warmer to cooler substancescooler substances.


Heat always moves from a warmer place to a cooler place.

“Hot” objects in a cooler room will cool to room temperature and “Cold” objects in a warmer room will heat up to room temperature: known as thermal equilibrium.

ENERGY TRANSFERENERGY TRANSFER

Hot water Cold water

(90. oC) (10. oC)

Fast Slow

GLOW STICK DEMONSTRATIONGLOW STICK DEMONSTRATION

What will happen to the glow stick when it is placed in hot water?

What will happen to the glow stick when it is placed in cold water?

How is temperature measured?Thermometer

In order to measure temperature accurately, what physical property is relied upon?Most objects EXPAND when their temperature increases

TEMPERATURETEMPERATURE

The first widely used temperature scale was devised by Gabriel Fahrenheit. Water freezing point: 32F

Water boiling point: 212F

Another widely used scale was devised by Anders Celsius.Water freezing point: 0C.

Water boiling point: 100C

TEMPERATURE SCALESTEMPERATURE SCALES

Conversion between Fahrenheit and Celsius Equations:

Example #1: An object has a temperature of 45C. What is its temperature in degree Fahrenheit? 113 F

Example #2: The temperature of a winter day is 14F. What is the temperature in degree Celsius? -10 C

TEMPERATURE SCALESTEMPERATURE SCALES

325

9

329

5

CF

FC

TT

TT

The zero point on the Fahrenheit scale was based on the temperature of a mixture of salt and ice in a saturated salt solution.

The zero point on the Celsius scale is the freezing point of water.

Both scales go below zero.

ZERO TEMPERATUREZERO TEMPERATURE

Kelvin Scale (Absolute Temperature Scale):

Examples: Water freezing point: 0C =273.2 K.Water boiling point: 100C = 373.2 K

KELVIN TEMPERATURE SCALEKELVIN TEMPERATURE SCALE

TK TC 273.2

Absolute Zero: the coldest possible temperature that can be reached; occurs when there is no more thermal energy in an object.It is not possible to reach absolute zero because you can never remove all of the heat from an object.

ABSOLUTE ZEROABSOLUTE ZERO

ABSOLUTE ZEROABSOLUTE ZERO

MISCONCEPTIONS ABOUT TEMPERATURE

https://www.youtube.com/watch?v=vqDbMEdLiCs

There are three ways energy transfer can take place. They are: conduction, convection, and radiation.

METHODS OF ENERGY TRANSFERMETHODS OF ENERGY TRANSFER

METHODS OF ENERGY METHODS OF ENERGY TRANSFERTRANSFER

Conduction: heat transfer through matter due to a temperature difference

For this method of heat transfer, it requires objects to come into direct contact

Conduction = CONTACT

CONDUCTIONCONDUCTION

Have you ever touched a pan on the stove and got burned? That was thanks to conduction.

Takes place when 2 objects in contact are at unequal temperatures

REMEMBER: REMEMBER: Energy transfer always takes place from warmer to cooler substances.

When you heat a metal strip at one end, the heat travels to the other end.

As you heat the metal, the particles vibrate, these vibrations make the adjacent particles vibrate, and so on and so on, the vibrations are passed along the metal and so is the heat. We call this? Conduction

A piece of cheese melts as heat is transferred from the meat to the cheese (Contact)

EXAMPLE OF CONDUCTIONEXAMPLE OF CONDUCTION

EXAMPLE OF CONDUCTIONEXAMPLE OF CONDUCTION

CONVECTIONCONVECTION

Convection: heat transfer by the movement of mass from one place to another; it can only take place in liquids and gases


Involves the movement of the heated substance itself

Convection is only possible if it is a fluid (liquid or gas) because the particles within solids are not as free to move

CONVECTION CURRENTCONVECTION CURRENT

Convection Current: the flow of a fluid due to heated expansion followed by cooling and contraction

http://http://www.absorblearning.cwww.absorblearning.com/media/item.action?om/media/item.action?quick=12p quick=12p

CONVECTION CURRENT AND EARTH CONVECTION CURRENT AND EARTH SCIENCESCIENCE

CONVECTION CURRENTSCONVECTION CURRENTS

Heating and cooling of a building involves convection currents: warm air expands and rises from vents near the floor; it then cools and contracts near the ceiling & sinks back to the floor

Examples of Convection:Air movement in a home A pot of heating water

EXAMPLES OF CONVECTIONEXAMPLES OF CONVECTION

Consider this - when you look at the road in the summertime on a hot day, you may notice that the air above the road looks “blurry” – this is convection taking place as the hot air directly over the road absorbs the heat from the road and rises. Although the explanation can be quite complex, convection can help explain why mirages are seen in the desert.


If conduction deals with solids and convection deals with liquids, how does heat arrive to Earth from the Sun?

There is very little matter in between the Earth and Sun.

QUESTIONQUESTION

RADIATIONRADIATION

Radiation: the transfer of energy by electromagnetic waves

A hot object radiates more energy than a cool object.

RADIATIONRADIATION

Radiation is different from conduction and convection because it does not involve the movement of matter; and, it is the only way heat is transferred that can move through empty space.

Examples of Radiation Fire Heat Lamps Sun

EXAMPLES OF RADIATIONEXAMPLES OF RADIATION

1. Obtain a popcorn popper. Place the popcorn kernels in the popper. Plug in/turn on the popper. Hot air will transfer heat to the kernels, making them expand and pop.

2. Put oil in the bottom of a pan. Cover the bottom of the pan with popcorn kernels. Place the pan on the stove and turn on the burner to medium heat. Cover the pan with a lid. Periodically shake the pan so the kernels move around in the oil.

3. Microwave a bag of microwave popcorn. #1: Convection, #2: Conduction, #3: Radiation

METHODS OF COOKING POPCORN: METHODS OF COOKING POPCORN: CONDUCTION, CONVECTION, OR CONDUCTION, CONVECTION, OR

RADIATION?RADIATION?

CONDUCTION, CONVECTION, CONDUCTION, CONVECTION, & RADIATION& RADIATION

Conductor: a material through which energy can be easily transferred as heat.Gases are poor conductors because their particles are far apart and the particle collisions necessary for energy transfer rarely occur.

CONDUCTORS AND INSULATORSCONDUCTORS AND INSULATORS

GOOD CONDUCTORSGOOD CONDUCTORS

Good conductors: metals such as copper and silver, along with gold aluminum iron steel brass bronze mercury graphite dirty water concrete

BAD CONDUCTORSBAD CONDUCTORS

Bad Conductors: Certain solids like rubber and wood glass oil asphalt fiberglass porcelain ceramic quartz (dry) cotton (dry) paper plastic air diamond pure water

INSULATORINSULATOR

Insulator: a material that is a poor energy conductorGood insulator: wood

THESE ARE PICTURES OF THESE ARE PICTURES OF CONDUCTORS AND INSULATORSCONDUCTORS AND INSULATORS

Conductors Insulators

1. How does the average kinetic energy of an object relate to its temperature?

1. Temperature is proportional to average kinetic energy; as the kinetic energy of an object increases, its temperature will increase.

REVIEW QUESTIONSREVIEW QUESTIONS

2. If a cup of coffee and a popsicle were left on the table in this room, what would happen to them? Why?

2. The cup of coffee will cool until it reaches room temperature. The popsicle will melt and then the liquid will warm to room temperature.


3. Why does hot air rise and cool air sink?

3. In warm air, the molecules move apart, so it is less dense and rises. In cooler air, the molecules move closer together, so it is more dense and sinks.


4. T or F: Radiation requires particles to travel through.

5. T or F: Radiation travels at the speed of light.

6. T or F: Radiation can travel through a vacuum.


7. Suppose I have 2 objects: a coat and a metal hanger. Both objects were left in this classroom overnight. The temperature of the classroom is 68◦F, therefore, both objects are the same temperature (thermal equilibrium). Why does the hanger feel colder to the touch than the coat?


8. When you hold a piece of ice in your hand, what causes it to melt?

8. The temperature of the ice is lower than your hand; therefore, the molecules in the ice move more slowly than those in your hand. As the molecules on the surface of your hand collide with those of the ice, energy is transferred from your hand to the ice.


energy transfer thermal energy & em spectrum unit 9 section 1 notes

Documents

room temperature

temperature differencefor

temperature differences

coldest possible temperature

freezing point of water

form of thermal heat

ways energy transfer

fahrenheit scale