TEMPERATURE
Background Galileo invented the first device for measuring temperature in Called thermometer because thermo means heat, and meter means a measuring device. Thermometers we use today contain a liquid that expands and contracts when heated.
Temperature Temperature is a degree of hotness or coldness the can be measured using a thermometer. It's also a measure of how fast the atoms and molecules of a substance are moving. Temperature is measured in degrees on the Fahrenheit, Celsius, and Kelvin scales.
Measuring Temperature A relative idea about temperature is that it tells you how hot or cold something is. This can be acomplished by using our senses: – Touch (sensitive nerve endings on your skin can detect changes in temperature) – Sight (the color of the material giving off heat) Relative ways to determine the temperature are not always reliable or safe. Baffle your skin page 193
What did you find out? 1. Was there any difference in your observations in steps 2 and 3? If there was, suggest a reason why. 2. Use your observations in this activity to explain how the same air temperature can seem warm in the winter and cool in the summer.
Activity Collect data using a thermometer to measure the temperature of various items. How to use a thermometer: – Do not touch the bulb – Do not hold in your hand for a long period of time. Heat will transfer from body to the thermometer.
Temperature of Items ItemTemperature Outside Room Iced water Warm water Boiling water Body
Temperature Scales Early thermometers and their inventors: Anders Celsius – 1742 used the 1st precise scale – Used degree as the unit of temperature – 0 indicated when ice melts at sea level – 100 indicated when liquid boils at sea level – The region between these two extremes was separated into 100 equal units or degrees – D96C085603F74599&playnext=1&playnext_from=PL&index=19 D96C085603F74599&playnext=1&playnext_from=PL&index=19
Pressure Did you know that pressure can affect the freezing and boiling points of water? High pressure causes ice to melt below zero degrees. Low pressure enables water to boil at a temperature below 100 degrees. On the top of Mt. Everest, water boils at 69 degrees!
Lord Kelvin Developed the Kelvin scale Absolute zero is the coldest possible temperature –273 degrees The markings on the scale are not called degrees but called Kelvins. 0 degrees celsius = -273 degrees Kelvin
The Right Device for the Job Measuring different extremes of temperatures means using different types of devices to measure these extremes. The thermometers used for this purpose have: A sensor- a material which is affected by changes in some feature of the environment, such as temperature A signal – provides information about the temperature, such as an electric current. A responder – which indicates the data with a pointer, light or other mechanism using the signal.
Thermocouple When heat is applied to one end an electric current is produced. The amount of current depends on the temperature and types of wires. This current can turn on and off a switch or valve. Used to measure very high temperatures Poor accuracy with low temperatures
Thermocouple Diagram A junction between two dissimilar metals produces a voltage. The sensing junction - produces a voltage that depends upon temperature. Where the thermocouple connects to instrumentation (copper wires) you have two more junctions and they also produce a temperature dependent voltage. Those junctions are shown inside the yellow oval.
The Bimetallic Strip A bimetallic strip is made of two different metals joined (fused) together, often formed into a coil When heat is applied to the end, one of the metals will expand faster than the other and the coil can operate a switch or valve just as a thermocouple does.
The Recording Thermometer When a bimetallic coil strip is attached to a long arm lever, with a marker at the end and a drum that has graph paper, a recording thermometer can be made. This instrument works much the same as a seismograph.
The Infrared Thermogram If an object is warmer than absolute zero it gives off infrared (IR). The infrared radiation can be photographed with special films or detected by special sensors that displayed colored images. The brightness or color of the image indicates the temperature of the object.
Infrared Thermometer (thermogram) Converts infrared radiation into colors that can interpret a temperature difference.
Watch Bill Nye -Heat