Temperature and Thermometers

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Temperature and Thermometers

The Temperature of an object is a measure of the hotness or coldness of that object. An alternative way to think of temperature is to say that “the temperature of an object is a number – on some manmade scale – that indicates the hotness of the object”. ‘Hotness’ in turn is a measure of the kinetic energy of the molecules of the material. Note: You must use the term ‘hotness’.*

The SI unit of temperature is the Kelvin (K)*

Relationship between degrees Celsius and Kelvin*:

Thermometric Properties
A Thermometric Property is any physical property that changes measurably with temperature. Note: You must use the term ‘measurably’.

Examples of thermometric properties:
Length of a column of liquid, e.g. mercury and alcohol thermometers, •Electrical resistance (see chapter 23),
Colour (colour ‘strips’ are sometimes used by nurses and placed against a person’s forehead), •Emf of a thermocouple (emf is a fancy word word for ‘voltage’), •Volume of gas at constant pressure,

Pressure of a gas at constant volume.

Disagreement between thermometers
Two different types of thermometer will give slightly different readings at the same temperature.* This means we need to agree on one particular thermometer to have as a standard.

Practical Thermometers
Clinical thermometer
Oven thermometer
Temperature gauge in a car

Clinical thermometer; Two Main Features:
Short range because temperature of the human body doesn’t vary much either side of normal body temperature (37.60 C). A kink to prevent the liquid falling back down when the thermometer is removed from the mouth and held vertically.

Experiment: Using a thermometric property to measure temperature* 1.Note the value of the thermometric property in melting ice (00 C) and also in boiling water (1000 C). 2.Plot these two points on a graph and draw a straight line joining them. 3.For an unknown temperature, note the thermometric property and use the graph to calculate the corresponding temperature.

Mandatory Experiment: To plot a calibration curve for a thermometer using a mercury thermometer as a standard.
Leaving Cert Physics Syllabus

ContentDepth of TreatmentActivitiesSTS

Concept of temperatureMeasure of hotness or coldness of a body. The S.I. unit of temperature is the Kelvin.
Celsius scale is the practical scale of temperature.
T /0C = T /K – 273.15

Thermometric PropertiesA physical property that changes measurably with temperature.Demonstration of some thermometric properties: •length of liquid column, e.g. length of mercury column
emf of thermocouple
Pressure of a gas at constant volume
Volume of a gas at constant pressure

ThermometersThermometers measure temperature.
Two thermometers do not necessarily give the same reading at the same temperature. The need for standard thermometers – use any commercial laboratory thermometer as a school standard.Graduate two thermometers at ice and steam points. Compare values obtained for an unknown temperature, using a straight-line graph between the reference points.Practical thermometers, e.g. •clinical thermometer

oven thermometers
boiler thermometer
temperature gauge in a car.

Extra Credit
* You must use the term ‘hotness’
So why can’t we say that “the temperature of an object is a measure of how hot or cold an object is”? ‘Hot’ is a vague term. Does it refer specifically to temperature, or to the amount of heat in the object? After all, a litre of water at 1000 Celsius has twice as much heat as half a litre of water at 1000 Celsius. ‘Hotness’ is the physicists way of overcoming this potential confusion.

*The SI unit of temperature is the Kelvin (K)
SI stands for ‘Standard Internationale’ (French). Basically it’s a system of units (incorporating the metric system) which connects up all the main physical quantities, and which has been agreed by all scientists (but not...
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