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Heat. Temperature and Heat. What is temperature??. Some Definitions. The degree of hotness or coldness of a body or environment. A measure of the warmth or coldness of an object or substance with reference to some standard value.
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Temperature and Heat What is temperature??
Some Definitions The degree of hotness or coldness of a body or environment. A measure of the warmth or coldness of an object or substance with reference to some standard value. A measure of the average kinetic energy of the particles in a sample of matter, expressed in terms of units or degrees designated on a standard scale. A measure of the ability of a substance, or more generally of any physical system, to transfer heat energy to another physical system. Any of various standardized numerical measures of this ability, such as the Kelvin, Fahrenheit, and Celsius scale.
Temperature is a reflection of what the thermometer reads. A typical thermometer has a liquid encased into a glass column.
The liquid in the thermometer will expand as the temperature increases. The increase in volume is thus due to a change in height of the liquid within the column. The increase in volume, and thus in the height of the liquid column, is proportional to the increase in temperature. Suppose that a 10-degree increase in temperature causes a 1-cm increase in the column's height. Then a 20-degree increase in temperature will cause a 2-cm increase in the column's height.
Temperature Scales A centigrade thermometer has 100 divisions or intervals between the normal freezing point and the normal boiling point of water. Today, the centigrade scale is known as the Celsius scale, named after the Swedish astronomer Anders Celsius who is credited with its development.
The Fahrenheit scale is named in honor of German physicist Daniel Fahrenheit. The normal freezing point of water is designated as 32 degrees and the normal boiling point of water is designated as 212 degrees in the Fahrenheit scale.
Temperatures expressed by the Fahrenheit scale can be converted to the Celsius scale equivalent using the equation below: °C = °F/1.8 - 32° Similarly, temperatures expressed by the Celsius scale can be converted tot he Fahrenheit scale equivalent using the equation below: °F= 1.8•°C + 32°
The Kelvin temperature scale, which is the standard metric system of temperature measurement and perhaps the most widely used temperature scale used among scientists. The degree symbol is not used with this system. So a temperature of 300 units above 0 Kelvin is referred to as 300 Kelvin and not 300 degree Kelvin.
Conversions between Celsius temperatures and Kelvin temperatures (and vice versa) can be performed using one of the two equations below. °C = K - 273.15° K = °C + 273.15
The lowest temperature possible is 0 on the Kelvin scale. Generally substances contract as they cool. If you lowered the temperature of an ideal gas so that the particles wouldn't interact with each other and contract to have zero volume, you would reach the temperature of Absolute Zero. Absolute zero is 0 on the Kelvin and -273 on the Celsius scale.
Other Types of Thermometers Bimetallic thermometers use two different metals joined into one strip. As the temperature changes, the two metals expand at different rates causing the strip to bend. The larger the bend the greater the temperature change.
Bimetallic strips are often coiled with one end attached to a pointer and the other end fixed securely.
Thermostats in most homes often have a bimetallic strip or coil attached to a mercury switch. When the temperature cools down, the coiled strip bends more causing the glass bulb to angle towards the wire leads. The mercury slides to the wire leads, connecting the circuit and an electrical current is passed on to the furnace.
A thermocouple contains 2 different metal wires joined at two points. One point, called reference junction, is a known temperature (eg. normal air or cool water) The other point, called sensing junction, is where the temperature is to be taken. If the temperature at the 2 junctions is different, an electrical current is produced, which is translated into a temperature reading. The greater the temperature difference, the more current produced. Thermocouples are used in natural gas furnaces and water heaters.
Thermistors are thermally sensitive resistors made of metal oxides (semiconductors). They come in glass bead, disc, chips and probe forms. The thermistor is connected to an electric current. When the temperature of the thermistor increases, the electric current increases and is translated into a temperature reading. Thermistors are fast and accurate. They can record up to 0.0005°C of a temperature change. Thermistors are commonly used in electronic thermometers in hospitals and automotive coolant temperature gauges.
Kinetic Molecular Theory After centuries of questioning and puzzling over the nature of heat, scientists now believe that heat is linked to the way molecules move. Therefore they refer to this theory as the Kinetic Molecular Theory. This theory is helpful in describing temperature, heat, and thermal energy.
Some of the key features of this theory: All matter is made of atoms, which may combine to form molecules. Atoms and molecules are in a constant state of motion. Atoms and molecules exert an electrical force on each other. These forces are attractive when the atoms and molecules are closer together. If the atoms and molecules are too close together the force becomes repulsive. Solids maintain their shape and volume and the electrical forces cause solids to vibrate about a fixed, rigid position.
Liquids take the shape of their container, but have a fixed volume. Atoms and molecules move about quicker than in solids, so the attractive force between molecules is weaker. In a gas, atoms and molecules move about very quickly, and the attractive force is very weak. Atoms and molecules are further apart than in liquids and tend to move out in all directions. Gases do not maintain their shape or volume. Molecules have potential energy holding them together. They also have kinetic energy because of their motion.
Solid Crystal Attractive force causes molecules to vibrate but stay in a fixed position.
Liquids Attractive force is weaker in a liquid - - molecules are further apart and move about quickly.
Gas Attractive force is very weak in a gas - - molecules are far apart and move about very quickly.
Therefore: temperature is a measure of the average kinetic energy of the particles within a sample of matter.
A sample of matter consists of particles that can be vibrating, rotating and moving through the space of its container. So at the particle level, a sample of matter possesses kinetic energy. A warm cup of water on a countertop may appear to be as still as can be; yet it still has kinetic energy. At the particle level, there are atoms and molecules that are vibrating, rotating and moving through the space of its container.
As atoms move through space from one location to another. As they do, they encounter collisions with one another. These collisions result in changes in speed and direction. As a result, there is not a single speed at which the atoms move, but a range of speeds.
