Chapter 11 Flashcards
(12 cards)
What is internal energy?
U
Energy associated with the atoms and molecules in a system
Included kinetic and potential energy associated with random translational, roatational, and vibrational motion of the particles that make up the system
Slide 12 March 14
What is heat?
Transfer if energy between a system and its environment due to a temperature difference between them
Symbol Q is used to represent amount of energy transferred by heat between a system and environment
What is calorimetry?
When two objects at different temps are put in thermal contact and allowed to reach thermal equilibrium in isolation, then from conservation of energy; Qcold=-Qhot
ΣQ=0
Example slide 22 Mar 14
What are the 3 processes by which energy is transferred by heat?
Conduction- occurs within solids, liquids and gases
Collisions between atoms
If temperature is not uniform, then the atoms with more energy (at hot end) transfer energy to atoms with less energy
Slides 25-26 Mar 14
Convection- only occurs in fluids (liquids and gases)
Radiation- all objects emit thermal (electromagnetic) radiation
What is the R factor?
It’s equation?
Relates the rate of energy transfer per unit cross-sectional area
Directly proportional to thermal resistance so for equal cross sectional area the effective R-factor of stacked slabs is the sum of the R-factors of the individual slabs
R-factor=L/k = RA
P/A = ΔT/R-factor
What is thermal conduction?
Collisions between atoms
If temperature is not uniform, then the atoms with more energy (at hot end) transfer energy to atoms with less energy
Slides 25-26 Mar 14
What is thermal convection?
Transfer if energy by the macroscopic motion of the medium (convection currents)
Convection can occur in fluids (liquids and gases) but not solids
Convection can be natural or forced
Natural occurs due to the temperature-dependence of density and the buoyant force
Forced occurs when fans or pumps are used to circulate the fluid
Slides 24-25 Mar 19
What is the wind chill?
Wind chill index is related to the dependence of convective heat loss on the relative speed of a fluid and the surface over which it moves
Related to how cold you feel, reference air temperature in calm conditions that produces the same rate of heat loss
Wind does not actually produce a lower temp
What is thermal radiation?
All objects continuously emit (and absorb) thermal radiation
It is electromagnetic waves arising from the oscillations of electric charges (electrons and protons) in atoms
Can propagate through a vacuum
Slides 29-30 Mar 19
What is Wein’s law?
Emitted thermal radiation is distributed across a wide variety of wavelengths Peak wavelength (wavelength at which max power is emitted) decreases with increasing temperature
λmaxT = 2.898e-3 m•K
Slide 33 Mar 19
What is thermography?
Detection and mapping of thermal radiation
Used to detect buried survivors of earthquakes, diagnosis of tumours, injuries, fevers, etc.
Prediction of volcanic eruptions
Paths of warm ocean currents
Slides 14-16 Mar 21
What is the greenhouse effect?
The atmosphere is relatively transparent to the visible and near IR radiation coming from the sun
When the earth absorbs this radiation it re-emits in the far-IR, which the atmosphere absorbs. The atmosphere then re-radiates some of this energy back to the Earth’s surface
CO2, CH4, N2O, SO2, HFCs, and water vapour are efficient absorbers if far-IR radiation
Slides 18-20 mar 21
