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How do macroscopic observations provide a model of the microscopic properties of a substance?
How do macroscopic observations provide a model of the microscopic properties of a substance?
Macroscopic observations like temperature, pressure, volume, and phase (solid, liquid, gas) help build a molecular model of matter:
In solids, macroscopic rigidity suggests particles are tightly packed and vibrate about fixed positions.
In liquids, the ability to flow but maintain volume shows that particles are close together but can move past each other.
In gases, compressibility and expansion suggest particles are far apart and moving freely at high speeds.
Temperature readings (Kelvin or Celsius) correlate with the average kinetic energy of particles: Kelvin temperature∝average kinetic energy of molecules
Density measurements () reveal how closely packed the particles are in different states of matter.
Phase changes (e.g., melting, boiling) observed at constant temperature imply changes in intermolecular potential energy, not kinetic energy.
How is energy transferred within and between systems?
How is energy transferred within and between systems?
Conduction: Transfer of thermal energy through collisions of particles (higher kinetic energy particles transfer energy to lower energy ones); occurs mainly in solids.
Convection: Transfer via bulk movement of fluid; hot fluid rises (lower density), cold fluid sinks (higher density), creating circulation.
Thermal Radiation: Emission of electromagnetic waves (mainly infrared); no medium required.
How can observations of one physical quantity be used to determine the other properties of a system?
How can observations of one physical quantity be used to determine the other properties of a system?
Measure temperature gradient and rate of conduction to find a material’s thermal conductivity.
The rate of energy transfer can indicate properties like thermal conductivity if studied carefully.
Measure luminosity and apparent brightness (intensity observed from Earth) and thus determine the distance to a star.
Measure the peak wavelength in a blackbody spectrum and use Wien’s law to find the temperature of a star or other radiating body.
Knowing temperature and surface area allows us to predict radiated power and thermal behavior.
Measuring temperature change ΔT and knowing the specific heat capacity c allows you to find the thermal energy transfer Q.
Observing a phase change at constant temperature, and measuring the energy absorbed or released, gives information about the latent heat
Observing the direction of heat flow tells us which object has the higher temperature (since heat flows from higher to lower temperature).
Understandings
Understandings
molecular theory in solids, liquids and gases
density
that Kelvin and Celsius scales are used to express temperature
that the change in temperature of a system is the same when expressed with the Kelvin or Celsius scales
that Kelvin temperature is a measure of the average kinetic energy of particles
that the internal energy of a system is the total intermolecular potential energy arising from the forces between the molecules plus the total random kinetic energy of the molecules arising from their random motion
that temperature difference determines the direction of the resultant thermal energy transfer between bodies
that a phase change represents a change in particle behaviour arising from a change in energy at constant temperature
quantitative analysis of thermal energy transfers Q with the use of specific heat capacity c and specific latent heat of fusion and vaporisation of substances L
that conduction, convection and thermal radiation are the primary mechanisms for thermal energy transfer
conduction in terms of the difference in the kinetic energy of particles
quantitative analysis of rate of thermal energy transfer by conduction in terms of the type of material and cross-sectional area of the material and the temperature gradient
qualitative description of thermal energy transferred by convection due to fluid density differences
quantitative analysis of energy transferred by radiation as a result of the emission of electromagnetic waves from the surface of a body, which in the case of a black body can be modelled by the Stefan Boltzmann law where L is the luminosity, A is the surface area and T is the absolute temperature of the body
the concept of apparent brightness
luminosity L of a body
the emission spectrum of a black body and the determination of the temperature of the body using Wien's displacement law where max is the peak wavelength emitted.
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