1. Topic #2

2.  You probably think of temperature as a number that tells you how hot or cold something is  This topic will get more into the scientific picture of temperature  One way to figure a rough temperature is just to touch something  Some nerve endings in the human body are quite sensitive to temperature

3.  Health care workers can determine patient temperature by touching the forehead with the back of their hand  People who work with hot, glowing materials can estimate temperature by the colour of the light the materials give off  Astronomers can do the same with stars based on the colour of light they give off

4.  Thermometers are mechanical or electrical devices for measuring temperature  One of the earliest thermometers was invented around 1600 by Galileo  More portable liquid thermometer was made around 1700 but they were still lacking accuracy (scary, grumpy looking guy)

5.  Early thermometers were lacking scales – markings with numbers to indicate precise temperature  Modern thermometers have gradations or evenly spaced lines that allow you to read exact temperatures

6.  The temperature scale commonly used in Canada and many other countries is called the Celsius scale  This was developed by Anders Celsius (1701- 1744) – he used the degree as a unit of temperature  He based his standards for comparison on the properties of water  He assigned zero degrees to the temperature at which ice melts at sea level

7.  He assigned one hundred degrees to the temperature at which liquid water boils at sea level  He then spaced the region in between into 100 evenly spaced units or degrees  To calibrate thermometers you must do it at sea level with very pure water

8.  Salt water freezes above zero degrees  Pressure also affects freezing and boiling of water  Because of high altitude in Alberta, water will actually boil several degrees less than 100 o C  At the top of Mount Everest, water would boil at only 69 o C!!!!!!!

9.  Scientists needed a temperature scale that started at the coldest possible temperature or “absolute zero”  The new temperature scale was named the Kelvin scale – in honour of William Thomson (Lord Kelvin) 1824-1907  No one has cooled anything to absolute zero but it is predicted to be around -273.15 o C Measured in kelvins 0 o C=273.15K (what’s with the beards??)

10.  Do you think you could use a normal thermometer to measure the surface of the sun?  Special thermometers have been developed to measure extreme conditions or special situations  Each of these special thermometers contain a sensor – material which is affected by changes in temperature

11.  The sensor produces a signal – information about temperature, such as an electrical current  The signal affects the responder – a pointer, light or other mechanism that used the signal in some way

12.  In a thermocouple, wires made of two different metals are twisted together  When the wire tips are heated, a small electrical current is generated  The amount of current depends on the temperature of the wires  The current from the thermocouple can be used to turn on a switch or valve  They are used to measure extremely high temperatures where normal devices would fail as the liquid in them would boil

13.  The bimetallic strip is made of two different metals joined firmly together  As the strip is heated one metal expands more than the other  The strip is then forced to coil more tightly and the opposite occurs when cooled  Movement of the strip can operate a type of electrical switch  Usually used in furnaces, air conditioners, refrigerators, etc

14.  The recording thermometer uses a bimetallic strip that coils and uncoils as the temperature changes  One end of the strip is attached to a light metal lever that holds a special pen  The pen writes on a large drum lined with paper that rotates once every seven days and keeps track of temperature over a week

15.  Objects don’t have to be glowing red hot to give off radiation  Anything warmer than absolute zero gives off IR (infrared radiation) – similar to light but undetectable to your eyes  Infrared radiation can be photographed with special films or detected by sensors that display images on screens