Topic #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
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
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)
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
The temperature scale commonly used in Canada and many other countries is called the Celsius scale This was developed by Anders Celsius ( ) – 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
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
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!!!!!!!
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) No one has cooled anything to absolute zero but it is predicted to be around o C Measured in kelvins 0 o C=273.15K (what’s with the beards??)
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
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
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
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
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
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