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ch 14 Heat
concepts and formulas
45
Physics
Undergraduate 1
01/21/2013

Additional Physics Flashcards

 


 

Cards

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/kgC

 

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
Rvalues
Term

1.Rvalues 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
T/F radiation requires a medium.
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

give radiation formula

& unit

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 <T2

What will occur?

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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