# Shared Flashcard Set

## Details

ch 14 Heat
concepts and formulas
45
Physics
01/21/2013

Term
 heat  is a form of
Definition
 energy
Term
 1.Unit of heat is 2. convert cal to J 3.convert kcal to kJ
Definition
 1.calorie(cal) 2. 1 kcal * 4.186 x 103 J 3. 1 kcal= 4.186 kJ
Term
 1 cal is the amount of heat necessary to
Definition
 raise the temperature of 1 g of water by 1 Celsius degree.
Term
 Definition of heat
Definition
 Heat is energy transferred from one object to another because of a difference in temperature. *Remember that the temperature of a gas is a measure of the kinetic energy of its molecules.
Term
 Internal /thermal energy def
Definition
 sum total of all the energy of all the molecules in a substance
Term
 Temperature def
Definition
 measures molecules’ average kinetic energy
Term
 Internal energy of an ideal (atomic) gas formula
Definition
 u=3/2nRT   (remember this is kinetic energy in terms of temperature and moles of gas)
Term
 Internal energy: If the gas is molecular rather than atomic, what other energy needs to be taken into account as well? (2)
Definition
 rotational & vibrational kinetic energy
Term
 Specific Heat def
Definition
 The amount of heat required to change the temperature of a material
Term
 Specific Heat formula and unit
Definition
 Q=mcΔT where c=specific heat for the material unit: J/kg• C
Term
 Although Specific heats of gases are more complicated, they are generally measured  at (2)
Definition
 constant pressure (cP) or constant volume (cV).
Term
 Calorimetry – Solving Problems Closed system def
Definition
 no mass enters or leaves, but energy may be exchanged
Term
 Open system def
Definition
 mass + energy may transfer as well
Term
 Isolated system def
Definition
 closed system, no energy in any form is transferred      *heat lost = heat gained or  Energy OUT of one part = energy INTO another part e.g. kettle to the mug
Term
 You accidently leave a frying pan on the hot stove and get its very hot, almost 200C, 1.What happens when you dunk the pan in a few inches of cool water in the sink? 2.Will the water boil? 3.Will the final temp be midway btwn the initial temps of the water & the pan?
Definition
 1.The water will warm up a few degrees (10 to 12) but will NOT boil b/c the mass of water is mostly equal to the pan & iron has a SMALLER specific heat than water) (*compare this to the sizzle u hear when you place a drop of water on a hot pan) 3. As heat leaves the pan and enters the water the pan will experience a greater temp change (ten times more than water).
Term
 T /F: Energy is required for a material to change phase, even though its temperature is not changing.
Definition
 True
Term
 Heat of fusion, LF def
Definition
 heat required to change 1.0 kg of material from solid to liquid
Term
 Heat of vaporization, LV
Definition
 heat required to change 1.0 kg of material from liquid to vapor
Term
 The values for : Heat of fusion (LF) & vaporization, (LV) are also called?
Definition
 Latent Heat (involves changes in phase & the release of energy)
Term
 phase change equation
Definition
 Q=mL Q= heat added or released (J) total mass: kg L: latent heat (J/kg)
Term
 write the phase equation for the following situation:  water reduces from 20 C to 0C
Definition
 in this situation energy is being LOST Q=mwater cw (20 C-0 C) (Template)Q=mc (Ti-Tf)
Term
 write the phase equation for the following situation:  water is heated from 0C to 5 C
Definition
 in this situation energy is being GAINED Q=mwater cw (5C-0 C) (Template)Q=mc (Tf-Ti)
Term
 The latent heat of vaporization is needed for what 2 processes?
Definition
 evaporation &boiling (aka it takes a certain energy threshold for these processes to occur)
Term
 If sample A is at 40C and sample B is at 10C, which will one will require more energy to reach their boiling point?
Definition
 Sample B: The heat of vaporization of water rises slightly as the temperature decreases.
Term
 T or F: A  phase change to occurs because heat increases the kinetic energy of the individual molecules
Definition
 False, heat  breaks the close bonds between the individual molecules  so the next phase can occur.
Term
 Heat conduction formula & include unit
Definition
 Q/t= kA T1- T2              l A:area of object k:thermal conductivity constant unit: J/s T: can leave in C The heat flow per unit time
Term
 1.Materials with large k are called   2. small k are called
Definition
 1.conductors 2.insulators
Term
 Building materials are measured using _____ rather than thermal conductivity
Definition
 R−values
Term
 1.R−values formula 2.r values increse directly with ______
Definition
 1.R= l/k 2. material thickness
Term
 what is Convection?
Definition
 Convection occurs when heat flows by: the mass movement of molecules from one place to another. It may be natural or forced. ex. boiling pot of water hot water on bottom b/c stove is heating it, cold water on top, will  continue to cycle till all is hot
Term
 Give an example of forced convection
Definition
 Many home heating systems are forced hot-air systems; these have a fan that blows the air out of registers, rather than relying completely on natural convection.
Term
 Heat conduction def
Definition
 In heat conduction, energy is transferred from molecule to molecule by direct contact; the molecules themselves do not necessarily change position, but simply vibrate more or less quickly against each other. Heat conduction can be visualized as occurring through molecular collisions.
Term
 True/False: Convection and Conduction  require the presecence of matter as medium to carry  heat.
Definition
 True
Term
 Convection and Conduction  require the presecence of matter as medium to carry  heat to carry heat from ____ regions to _______ regions.
Definition
 hotter→ colder
Term
Definition
 false; the sun's energy transfer is in the form of heat and occurs over an EMPTY space   The most familiar example of radiation is our own Sun, which radiates energy in the form of heat to Earth  at a temperature of almost 6000 K
Term
Definition
 ΔQ/Δt= eσAT4 or if 2 temps: eσAT14-T24 unity: Watts (J/s) σ : Stefan-Boltzmann constant e: emissivity A: area T: Temp (K)
Term
 Stefan-Boltzmann constant
Definition
 5.67 * 10-8 W/m2 * K4
Term
 emissivity 'e '(define)
Definition
 number between 0 & 1 characterizing the surface of the radiating  material
Term
 1.black objects have an emissivity  2.shiny objects
Definition
 1. near 1 (they absorb nearly all the radiation) 2.near 0 (they reflect almost all the radiation)
Term
 why do we shiver?
Definition
 If you are sitting in a place that is too cold, your body radiates more heat than it can produce.   *You will start shivering and your metabolic rate will increase unless you put on warmer clothing.
Term
 T or False: A good absorber is a bad emitter.
Definition
 False, a good absorber is a good emitter.  EX. light colors absorb little or no radiation they are exposed to and thus emit very little. so ΔQ/Δt= 0 when T1=T2
Term
 T1 >T2 What will occur?
Definition
 the net flow of heat is from the object (T1) to the surroudings (T2) = the object cools
Term
 T1
Definition
 the net flow of heat is from the surroundings (t2) to the object(t1) = object's temp raises
Term
 formula of the rate of   energy absorbtion from the sun's rays
Definition
 ΔQ/Δt= (1000W/m2)eAcosθ     θ= angle btwn the sun's rays& a line perpendicular to the area A.   *cosθ effect is also responsible for the seasons.
Term
 Thermography
Definition
 the detailed measurement of radiation from the body – can be used in medical imaging. Warmer areas may be a sign of tumors or infection; cooler areas on the skin may be a sign of poor circulation.
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