Applied Physics Chap 51 Chapter 5: Temperature and Thermal Energy.

Applied Physics Chap 5 1

Chapter 5: Temperature and Thermal Energy


Temperature: a measure of the average Kinetic Energy of the particles contained in an object.

Thermometer: a device which uses the thermal expansion of a liquid to measure a substances temperature .

Reservoir

Capillary Tube

Thermal Expansion: the process by which materials expand in volume as their particles gain KE from heat and move faster.

Extra KE weakens the bonds between particles allowing them to pull further apart increasing their volume.


Temperature Scales:

Fahrenheit Thermometer

A mercury thermometer developed by Gabriel Fahrenheit in 1714.

He used the highest and lowest outdoor temperatures in his native Germany as 1000 and 00.

Water froze at 320 on his thermometer


Temperature Scales:

Celsius Thermometer

In 1742, Anders Celsius, a Swedish astronomer wanted to develop a scientific/metric based thermometer using easily measurable quantities. He choose 00 as the freezing point of water and 1000 as the boiling point of water.


Temperature Scales:

Kelvin Thermometer

A scale developed by William Thompson, Lord Kelvin, a famous English physicist in the mid 1800’s.

This scale was to be a scientific temperature scale with 00 as the lowest possible temperature (absolute zero).


Fahrenheit Celsius Kelvin

Comparison of Temperature scales

212Waterboils

100 373

Water Freezes

32 0 273

-459 -273 0

180 100 100

Abs. zero


Absolute Zero: the lowest possible temperature for matter is found to be about –273.15 0C. (-459 0F)

At this temperature all particle motion in a substance will stop (KE = 0).

This temperature has never been reached in the laboratory although scientists have gotten very close.

Kelvin Temp = Celsius temp + 273 degrees

Celsius Temp. = Kelvin Temp – 270 degrees


Celsius and Fahrenheit

The relationship between F and C is more complicated due to the different sizes of the degrees and the 32 degree offset for the freezing point of water. The Fahrenheit degree is on 0.56 the size of a Celsius degree,

F = 1.8 C + 32

C = ( F – 32 ) x 0.56


Thermal Expansion: the process by which most materials expand in volume, as its particles absorb KE and move faster.

Extra KE weakens the bonds (forces) that hold a substance together allowing the particles to pull further apart and thereby increasing the volume of the substance. This happens in all substances.

Examples of Thermal Expansion

a bar of metal getting longer when its heated,

a concrete roadway buckling on a hot summer day.

Liquid rising inside a thermometer.


Thermal Energy: Video


the total energy, kinetic and potential possessed by the particles that make up any material.

Thermal energy, like all types of energy, is measured in Joules.

Heat: is thermal energy in motion.

Thermal energy that flows from a hotter substance to a colder substance.

We measure heat by determining the amount of thermal energy that flows

Thermal Energy: the name given to energy in the form of heat.


Specific Heat Capacity “C” the quantity of heat required to raise the temperature of a unit mass (1 gram or 1 kg) of a substance by 1 degree Celsius.

Different substances have different capacities for storing thermal energy.

Metals generally need less energy to raise their temperatures by 1 degree C.

Liquids generally need more heat to raise their temperatures by 1 degree C.

For water: 4186 J of energy are required to raise the temperature of 1 kilogram of water by 1 0C.


Calculating the Heat gained or lost.

TE = m C T

Where: m is the mass of a substance in kilograms

C is the specific heat capacity

T is the temperature difference in 0C

T = Thot - Tcold

ΔTC

Qmand

ΔTC

QC,

mC

QΔT


Mechanisms of Heat Transfer

Conduction: the flow of heat by “direct contact” between two substances.

Heat moves between the stove and the teapot by conduction. Conduction also occurs between the bottom of the glass and molecules of water in contact with the bottom.


Conductor: materials that conduct heat. Metals are good conductors because heat is easily transferred through the atoms making up the metal.

Insulator: a material whose internal arrangement of atoms makes the transfer of heat difficult. Liquids and gases are generally good insulators because the bonds connecting particles are weaker and don’t readily transmit energy.

Examples of good insulators as are plastics, spun fiber glass and wood. Trapped air is often used as an insulator in clothing, home insulation etc.


Mechanisms of Heat transfer

Convection: involves the transfer of heat by bulk movement of particles. Convection occurs most often in fluids: liquids and gases but can under certain circumstances occur in solids like the rock in the interior of the earth.

Heat


Mechanisms of Heat transfer

Radiation: the transfer of heat energy by electromagnetic radiation.

Energy in the form of electromagnetic waves that can travel through air, water, and empty space.

Substantial amounts of radiation reach the Earth every second in the form of visible light and Infrared radiation (heat energy)


ConvectionWater carries heat to radiator

Heat transfer in an automobile engine

Air passing through radiator carries heat

away.

Convection:

Work done by the exploding fuel-air mixture

Hot exhaustcarries heat

through tailpipe

Convection

Conduction: Heat flows from

cylinder to Water jacket


About 40%, of the heat released by the explosive burning of the fuel-air mixture does work driving the piston downward and rotating the crankshaft. The other 60% of the heat must be removed to avoid overheating the engine as follows: Hot gasses exit the exhaust valve and travel through the

exhaust pipes to the outside air. Conduction moves heat through the cylinder wall and into

the cooling water which is pumped through hoses to the radiator and finally to the outside air.


Heating systems: systems that convert chemical energy from fuels like coal, gas, and oil into thermal energy that is used to head living spaces.

Convection transfers heat into living spaces by moving warm air, steam or hot water. Air then moves that heat around the room.Some of the thermal energy produced in the heater must be discharged into the atmosphere up a chimney and is lost.

Electrical heating systems transfer electrical energy into heat.

Insulation is one way of minimizing the amounts of energy that are lost to the atmosphere.


Heating Systems.


Cooling System: any device or process that uses mechanical energy to transfer thermal energy from interior living spaces to the outside.

Examples are refrigerator’s, air conditioners, freezers.Most systems use a motor to convert electrical energy into mechanical energy. Through the use of several physical processes, thermal energy can be moved from a cooler area to a normally warmer area like the outside on a hot day.


Kinetic Theory of Matter

All matter is made up of particles: either atoms or molecules

particles are in constant motion (Kinetic energy)

The amount of motion determines the strength of the electrical forces between the atoms of the substance.

The strength of the electrical forces determines the phase of the substance: solid, liquid, or gas.


Solids have a definite shape, as the particles are bound tightly together and a definite volume.

If the amount of particle KE is higher that than in a solid, the bonds are strained and cannot hold particles together as tightly. Particles are still bound together but can more around each other.

•Amorphous solids: no regular pattern to the atoms. Example: glass

•Crystalline solids: regular geometric arrangements of atoms bound together by electrical forces. Example: quartz crystal,

sulfur crystal


Liquids flow allows them to take the shape of their container so liquids have an Indefinite shape.

Liquid volumes will not change under ordinary conditions giving liquids a Definite volume

Liquid volumes increase as you add heat.

Heat adds extra KE that further weakens the bonds allowing the particles to move further apart.

Liquids are phases of matter with higher KE allowing particles to flow past each


Gases: exist as the phase of matter with even higher KE’s. The bonds between particles in gses are completely broken so each particle exists independently

gases have an indefinite volume and an indefinite shape, since they completely fill any container.

Plasma’s are gases with extremely high KE’s.

At these energy levels, electrons are stripped away from the atoms leaving the atoms with overall positive charges mingling with the free negatively charged electrons. Therefore a plasma is a hot, electrical conductive gas.

Applied Physics Chap 51 Chapter 5: Temperature and Thermal Energy.

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