Heat and temperature


Heat is energy it can do work.Temperature is a man-made, arbitrary scale indicating which direction heat is flowing…is heat going into the system, temperature rising or is heat leaving the system, temperature declining.

Heat is measured with an instrument called a calorimeter. Heat is NOT measured with a thermometer. Temperature is measured with a thermometer. Heat is measured in Joules. Temperature is measured in degrees.

There are 3 thermometers which measure temperature. Recall that a thermometer is a man made scale simply indicating the direction of heat flow. It is also a relative measure of the motion of molecules in the system. there are Celcius scales, fahrenheit Scales, reamur Scale dan Kelvin Scale.

We can convert from one thermometer to another via these equations.

•        F = (9/5 x C) + 32 ( F = fahrenheit)

•        0,8 C = R                ( R = Reamurs)

•        K = C + 273            ( K = Kelvin)

Specific Heat

The specific heat is the amount of heat per unit mass required to raise the temperature by one degree Celsius. The relationship between heat and temperature change is usually expressed in the form shown below where c is the specific heat. The relationship does not apply if a phase change is encountered, because the heat added or removed during a phase change does not change the temperature.

Q = m c ∆T

The specific heats of most solids at room temperature and above are nearly constant, in agreement with the Law of Dulong and Petit. At lower temperatures the specific heats drop as quantum processes become significant.

Heat Transfer

The transfer of heat is normally from a high temperature object to a lower temperature object.

Heat Conduction

Conduction is heat transfer by means of molecular agitation within a material without any motion of the material as a whole. If one end of a metal rod is at a higher temperature, then energy will be transferred down the rod toward the colder end because the higher speed particles will collide with the slower ones with a net transfer of energy to the slower ones. For heat transfer between two plane surfaces, such as heat loss through the wall of a house, the rate of conduction heat transfer is:

Q = heat transferred in time

k= thermal conductivity of the barrier

A = area

T = temperature

d = thickness of barrier

Heat Radiation

Radiation is heat transfer by the emission of electromagnetic waves which carry energy away from the emitting object. For ordinary temperatures (less than red hot“), the radiation is in the infrared region of the electromagnetic spectrum. The relationship governing radiation from hot objects is called the Stefan-Boltzmann law:

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s