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Temperature & Thermal Energy transfer (Callibrating a Thermometer…
Temperature & Thermal Energy transfer
Definitions
Temperature:
measurement of the average amount of kinetic energy in the molecules of a body
Heat
transfer of thermal energy from one region to another
Thermal energy
total kinetic and potential energy of ALL molecules in a body
Change
generates more change
is inevitable in systems
Thermometric properties
any physical property that changes measurably with temperature
they vary continuously and linearly wth temperature
as temperature changes, physical property changes uniformly and continuously
Thermometric Properties and Examples
volume of a fixed mass of liquid
e.g mercury in glass thermometer, alcohol in glass thermometer
electrical resistance of a piece of metal
resistance thermometer
electrical voltage or a electromotive force
thermocouple thermometer
Callibrating a Thermometer
Fixed Temperatures
every thermometer has two standard degrees of hotness and coldness called the steam point and the ice point
e.g 0 degrees celsius - 100 degrees celsius
Linearity in thermometer
Linear Graphs
ideal for using in thermometers
one unique volume at every temperature
Physical Properties of Thermometer
sensitivity
measures the amount of change in thermometric propensity per unit change in temperature
responsiveness
measures how quickly thermometer can register change in temp
temperature range
this denotes the minimum and maximum temperatures that the thermometer can measure
calculating temperature with a mercury- in glass thermometer
Kelvin Scale
[°C] = [K] − 273.15
[K] = [°C] + 273.15
calculating temperature with a resistance thermometer
Calculating Temperature with Thermocouple
thermal energy transfer
always flows from a region of higher temperature to a region of lower temperature
net flow of thermal energy only takes place when there is a difference in temperature
Conduction
mainly in solids
conduction occurs in liquids and gases as well but less effective as the particles are spread further apart and would therefore take a longer period of time
thermal energy without the flow of any material medium
unlike convection, the particles do not move from one region to another
transfer of thermal energy through matter
particles with more KE transfer KE to neighbouring particles via collision
in Metals, thermal energy is transferred through vibration of particles and free electron diffusion while on non- metals only vibration of particles occur.
Vibration of particles
particles that are being heated vibrate vigorously about their fixed positions
they collide with neighbouring partciles making them vibrate vigorously as well
thermal energy has been transferred
the particles on the cooler end begin to vibrate more vigorously
Free electron diffusion
free electrons at the heated end absorb thermal energy and hence gain kinetic energy
free electrons that gain kinetic energy move at greater speeds and move towards the cooler regions.
as the electrons move, they collide with the atoms in the cooler region, making them vibrate more vigorously.
Radiation
transfer of thermal energy via electromagnetic waves
TE is absorbed/emitted in the form of radiation
molecules absorb EM waves in the form of molecules and electron vibrations
does not require a medium to occur
can occur in vacuums
darker colours are better radiators
they absorb and emit heat faster
Convection
currents in a fluid due to a difference in density
only in liquids and gases as it involves the bulk movement of the fluid that carries thermal energy
As hot air gains heat, the particles begin to spread further apart as they become less dense and their volumes increases. As the hot air starts to cool down, the particles become more compact and more dense, causing the volume to decrease, therefore cold air sinks.
Thermal Equilibrium
when there is no net gain or loss of thermal energy between two bodies
