Physics

17.5 Change of Phase
* Depending on the specific heat if the substance, the rise in temperature is directly proportional to the quantity of heat supplied and inversely proportional to the mass of the substance.
* During a change of phase, the temperature is remained constant.

* The change of phase from solid to a liquid is called fusion, ant the temperature at which this changeoccurs is called the melting point.
* The quantity of heat required to melt a unit mass of a substance at its melting point is called the latent heat of fusion for that substance.
* The latent heat of fusion Lf of a substance is the heat per unit mass required to change the substance from the solid to the liquid phase at its melting temperature.

* The term latent arises from the factthat the temperature remains constant during the melting process.

* The change of phase from liquid to vapor is called vaporization, and the temperature associated with this change is called the boiling point of the substance.
* The quantity of heat required to vaporize a unit mass is called the latent heat of vaporization.
* The latent heat of vaporization Lv of a substance is the heatper unit mass required to change the substance from a liquid to a vapor at its boiling point temperature.

* If should be noted that the Btu per pound (Btu/lb) equivalents can be obtained by multiplying the value in cal/g by 9/5.

* In condensation (vapor returns to its liquid phase) a vapor gives up an amount of heat equivalent to the heat required to vaporize it. Thus, the heat ofcondensation is equivalent to the heat of vaporization. (The difference lies in the direction in which the heat is transferred).

* When heat is removed from a liquid, its temperature will drop until it reached the temperature at which it melted .As more heat is removed, the liquid returns to its solid phase. This process is called solidification or freezing. The heat of solidification isexactly equal to the heat of fusion. (The difference is that heat is either absorbed or released.)

* To change from the solid phase directly to the gaseous phase without passing through the liquids phase. This is called sublimation. The quantity of heat absorbed per unit mass in changing from a solid to a vapor is called the heat of sublimation.
Chapter 18 Transfer of Heat
18.1 Methods of HearTransfer
* The three principal methods by which heat is transferred: conduction, convection, and radiation.

* Conduction is the process in which heat energy is transferred by adjacent molecular collisions throughout a material medium. The medium itself does not move.

* Convection is the process by which heat is transferred by the actual mass motion of a fluid. Differs fromconduction because the material medium is moving

* Radiation is the process by which heat is transferred by electromagnetic waves. These waves travel at the speed of light (3x10 to the 8 m/s) and require no material medium for their passage.
18.2 Conduction
* When two parts of a material are maintained at different temperatures energy is transferred by molecular collisions from higher to lowertemperature. This process of conduction is also aided by the motion of free electrons,

* General observations concerning the conduction of heat:
1. The quantity of heat transferred per unit of time is directly proportional to the temperature difference between the two faces.
2. The quantity of heat transferred per unit of time is directly proportional to the area of the slab.
3.The quantity of heat transferred per unit of time is inversely proportional to the thickness of the slab.
* The proportionality constant k is a property of the material called its thermal conductivity.
* Substances with a large conductivity are good conductors of heat, whereas substances of low conductivity are poor conductors or insulators.
* Thermal conductivity of a substance is a...