Temperature Physics 102 Professor Lee Carkner Lecture 2

PAL #1 Welcome  How does the P,V and T of the material inside the can change?   Describe the heat flow   How could you measure the work?   Weigh cap and measure height

Temperature  How does temperature manifest itself?   e.g., the height of a column of fluid   We still don’t know what temperature is

Thermal Equilibrium  Build a device that changes properties with temperature in an easily apparent way   Now put the thermoscope in a cup of water  When the thermoscope stops changing, it and the water are in thermal equilibrium    Two bodies at different temperatures placed together will exchange heat until they are in thermal equilibrium (and thus at the same temperature)

Zeroth Law of Thermodynamics  You can tell if two objects are in TE if when placed together their properties don’t change or   Zeroth Law of Thermodynamics 

Thermometers  In order for a thermoscope to be a thermometer it needs to be calibrated  Example: the Celsius scale   Put it in ice and mark the height of the column as 0   Fill in the numbers 1-99 (in even intervals) in between   Only tells you temperature relative to the freezing point of water

Types of Thermometers  Glass tube  Physics: Increase of length with increasing temperature  Pros:  Cons:  Resistance  Physics: Electrical resistance increases with increasing temperature  Pros:  Cons:  Dial  Physics: Increased bending of bi-metal strip with temperature  Pros:  Cons:  Radiation  Physics: Change in type and amount of radiation emitted with temperature  Pros:  Cons:

Temperature Scales  Gabriel Daniel Fahrenheit invented the mercury thermometer in 1714   Anders Celsius introduced his scale is 1742   William Thomson, Lord Kelvin, determined from theory that minus degrees Celsius is the coldest it can get

The Kelvin Scale  In science we normally use the Kelvin scale   Tells you temperature relative to absolute zero, the coldest anything can get   No negative numbers  T C = T K T F = 9/5 T C +32  A temperature change of 5 Celsius degrees is equal to a temperature change of 9 Fahrenheit degrees

Thermal Expansion  Heating an object causes it to expand   Why?   The degree of expansion depends on the change in temperature and the coefficient of expansion  We can measure temperature and look up coefficient of expansion

Linear Expansion  The degree to which the length of an object changes is given by:  L = L   T   This applies to all dimensions of a solid length, width and height   If the linear dimensions of a solid change then the volume must change:  V = V   T 

Thermal Expansion and Thermometers   Consider two strips of metal with different coefficients of linear expansion attached together (bimetal strip)   This principle is used in dial thermometers and thermostats

Next Time  Read: ,  Homework: CH 13, P 10, 11, CH 14: 9, 33  Note that you might have to look up values in the textbook  Watch units!