Lecture 6 - Temperature Flashcards
Why ar etemperature measurements important?
Because at different temperatures substances have different properties
What types of thermometer are the ?
Liqud and metal expansion, electrical resistance & Thermoelectricity
How does liquid expansion work?
Liquid confined in thin tube expands linearly with the rise of temperature e.g. mercury or alcohol
How does metal expansion work?
a bimetallic strip is heated. the metals have different expansivity therefore one bends more than the other in direct correlation with the temperature
How does Electrical resistance work?
with a rise in the most metals have an increase in electrical resistance given by:
Rt = R0*(1+at)
a=T coefficient of resistance
How do thermistors work?
They use the same principle as metal electric resistors but provide a much larger resistance change with temperature
What happens to a thermistor output with an increase in temperature?
it decreases
Thermistor output equation?
Rt = Ke^beta/T
what is Thermoelectricity
When electrical and thermal energy convert from one to the other
What is the Seebeck effect?
When a pair of metals are formed into a loop with 2 junctions at different temperatures a current flows related to temperature.
Whats a thermopile?
When groups of thermocouples are connected in series and the e.m.fs produced are added together. sometimes with ten or more hot junctions
