Heat & Temperature Grade 7 Science - Unit 2 Pgs 104-225
4.1 Temperature PTemperature is the measure of how much heat is in a substance. PTemperature is measured in degrees Celcius ( C) PIt is difficult to judge how hot or cold something is by touching or looking at it. A better way is to measure the temperature of the object.
PTo measure temperature accurately we use a thermometer. P The Celcius scale is the most frequently used scale for measuring temperature.
4.2 Temperature Galileo P Hundreds of years ago, there was no way to measure temperatures exactly... only estimates. P In 1596, Galileo, an Italian scientist invented the thermoscope. P A thermoscope is a device that detects changes in temperature but does not have a temperature scale.
Thermometer P The word thermometer is made from two words: Thermo - meaning heat
P Normal human body temperature is 37 C. When you get a fever, that is the body fighting infection. Raising the body s temperature kills bacteria, but if it goes too high, it can cause damage, especially to the brain. It is also dangerous when the body temperature goes too low. This is called HYPOTHERMIA. (Hyperthermia - too high) P Accurate temperature measurement is important: When measuring body temperature for fever. We use a special type of thermometer with a constriction above the bulb. At a weather station For baking cakes and cookies
The Celcius Scale P Invented by Anders Celcius scientist, in the 1700's, a Swedish P He made his scale by marking the freezing point of pure water as 0 and the boiling point of pure water as 100. P He divided the distance between these two points by 100 degrees and used the symbol
PHe proposed a new temperature scale that started at absolute zero and had the units that were the same size as the Temperature The Kelvin Scale P In the 1800's, William Thompson (AKA Lord Kelvin), while studying different gases, developed the idea that there is a Coldest possible temperature - absolute zero
Bimetalic Strip This strip is made up of two different metals that expand by two different amounts when heated. - It is an experiment that demonstrates thermal expansion. Two metals with different thermal expansion coefficients are bonded together and when heated, one will expand more than the other, causing the strip to bend to one side. No matter which way you direct the flame, the metal which expands more will bend in the same direction. This is used as a thermometer because the more intense the heat, the bigger the curve in the metal.
Thermometer P When a thermometer is built or made, it must be calibrated. (P. 125) PMost temperature scales are based on TWO fixed points Freezing point of fresh water C( 0) Boiling point of fresh water ( 1C00)
Types of Thermometers P 1. Clinical Thermometer Measures body temperature Has a constriction above the bulb. As liquid is warmed by patient s body heat, it expands past the constriction and rises up the bore so the temperature can be read. After the temperature has been taken, the liquid cools and contracts, but the liquid does not move past the constriction. You must shake the thermometer to get the liquid to move down.
Types of Thermometers P 2. Thermostat Measures temperature in an appliance or room It switches the appliance on or off at a pre-set temperature. Set the thermostat at 20 Celcius... if the temperature goes above 20 C, the thermostat causes the heater to shut off. When the temperature goes below 20 C, the thermostat causes the heater to turn on.
Thermostats
Types of Thermometers P 3. Thermocouple A thermometer that uses electricity to measure temperature It contains two different metal wires that are joined at one end or COUPLED The other ends are joined to a meter that measures electricity The amount of electricity that passes through the wires varies depending on the temperature These types of thermometers are used for places where people cannot go (inside computers, smokestacks, volcanoes, etc.)
Thermocouple
Types of Thermometers P 4. Resistance Thermometers P Operates on electricity, just like a thermocouple, but it can be used in even higher temperatures than a thermocouple. In this kind of thermometer, a platinum wire is used.
Types of Thermometers P 5. Optical Thermometer P Heat is a form of light... infrared light.the amount of infrared light given off by an object can be detected using an optical thermometer. P Infrared Thermogram - special type of photograph that shows differences in temperature.
Thermometers Calibrating a Thermometer P 1. Place the bulb of the thermometer in a mixture of pure water and ice. P 2. Observe the colored liquid until it no longer moves P 3. Mark this point as 0 degrees Celcuis. P 4. Remove thermometer, and place bulb in boiling water. P 5. Observe the colored liquid unitl it no longer moves. P 6. Mark this point as 100 degrees Celcius. P 7. Equally divide into 100 spaces (each space is one degree.)