Chapter 6 Heat is transferred from one place to another by three different processes
6.1 How Heat is Transferred I. Conduction P Conduction is the transfer of energy through matter from particle to particle. It is the transfer and distribution of heat energy from atom to atom within a substance. For example, a spoon in a cup of hot soup becomes warmer because the heat from the soup is conducted along the spoon. Conduction is most effective in solids-but it can happen in fluids.
Conduction
How Heat is Transferred P Convection is the II Convection transfer of heat by the actual movement of the warmed matter. Heat leaves the coffee cup as the currents of steam and air rise. Convection is the transfer of heat energy in a gas or liquid by movement of currents. (It can also happen in some solids, like sand.) P Convection Currents are created when heated gas (ex. air) or liquid (ex.water) rises and cooler gas or liquid drops back down.
Convection Hot water rises, cools, and falls. Heated air rises, cools, then falls. Air near heater is replaced by cooler air, and the cycle repeats. This creates a convection current. What if coils were at the bottom?
How Heat is Transferred P Radiation - Electromagnetic III. Radiation waves that directly transport ENERGY through space. Sunlight is a form of radiation that is radiated through space to our planet without the aid of gases,liquids or solids. The energy travels through nothingness! P Radiation is also transmitted through air. This is the reason you can feel the heat of a campfire from the side.
How Heat is Transferred Waves P You cannot see electromagnetic waves because they are not made of matter like the waves in the ocean. PElectromagnetic waves can carry energy through empty space or air. P The heat you feel from the Sun, a fire or the hot burner on your stove are transmitted by electromagnetic waves.
How Heat is Transferred P Radio waves Types - carry of Electromagnetic radio and television Waves - radiation signals P Microwaves - carry information to and from satellites P Infrared waves - mostly responsible for transmitting heat P Visible light - electromagnetic waves that can be detected by our eyes P Ultraviolet waves - invisible to our eyes, these are the waves from the Sun that cause sunburn P X-rays - used to make images of bones P Gamma Rays - radioactive waves. Can do serious damage to living tissue.
How Heat is Transferred Absorbing Radiant Energy P Different substances react differently to radiant energy P If the substance absorbs radiant energy, it gets warmer P If the substance reflects radiant energy, it does not get as warm P The darker the color, the more radiant energy that is absorbed ex. A dark shirt will be warmer on a summer day than a light shirt. P If radiant energy passes through a substance, very little energy is absorbed. Ex. glass
How Heat is Transferred Absorbing Radiant Energy PAll forms of electromagnetic radiation works this way. PThat is, when a surface absorbs any sort of electromagnetic radiation, it gets warmer
6.2 Conductors and Insulators PConductor - materials which permit heat energy to flow freely from atom to atom and molecule to molecule. An object made of a conducting material will permit heat energy to be transferred across the entire surface of the object. PThermalConductivity - the rate at which a substance conducts heat. Examples of conductors - metals,graphite, water and the human body
Conductors and Insulators PInsulator - materials which do not allow the free flow of heat energy from atom to atom and molecule to molecule. The particles of the insulator do not permit the free flow of heat energy; subsequently heat is seldom distributed evenly across the surface of an insulator. Example of insulators - a vacuum,wood, plastic, styrofoam, air
Conductors and Insulators A Vacuum A vacuum is a situation where there are no gas particles present. That is, all of the air is removed. Since there are no particles present, neither conduction nor convection can occur since both these methods of heat transfer, require particles to take place. A Thermos has a vacuum between the outside plastic and the inside glass section. The inside glass section is also silvered to act as a mirror to reflect back any heat radiation.
Diagram of a Thermos
Conductors and Insulators R-Value P All insulators are rated on their ability to resist heat transfer. This is called the R-value. PThe higher the R-value, the better the insulating properties of the substance. PWhen determining the R-value of the walls in a house, you must add up all the R-values of each layer. PA single pane of glass does not have a very high R- value, but two panes with air or argon gas between them has a much higher R-value.
6.3 Temperature vs Heat P Average Kinetic energy is the average amount of heat energy of all particles in a substance. P Total Kinetic Energy is the sum of the heat energy of all the particles in a substance. P Specific Heat Capacity is the amount of heat energy needed to raise the temperature of 1.00g of a substance by 1.00 degrees C.
Temperature vs Heat Average Kinetic Energy P Example of Average Kinetic Energy Let s say you have 100 particles in a liquid. Each particle has 2 Joules of heat energy. To get the average you add up all the particles and divide by 100 (that is add up 2 one hundred times to get 200 Joules and divide by 100 to get an average kinetic energy of 2 Joules per particle for the liquid) Temperature is a measure of average kinetic energy.
Temperature vs Heat Total Kinetic Energy P Example of Total Kinetic Energy To get the total kinetic energy of the same liquid, you just add up the amount of energy in each particle. So at 2 Joules each for 100 particles that would give you a total kinetic energy of 200 Joules. This is a measure of the amount of heat in a substance.
Temperature vs Heat P If this liquid had a temperature of 40 degrees Celcius and you were to pour half into another beaker, the temperature would stay the same, the average kinetic energy (100 Joules divided by 50 = 2 Joules) would stay the same, but the total kinetic energy would be half (50 particles at 2 Joules each equals 100 Joules total)
Temperature vs Heat Specific Heat Capacity P The Specific Heat Capacity of water is higher than most substances. P This is why the ground will heat up more than water when they are exposed to the same amount of sunlight. P Since heat can only be transferred through the ground by conduction (which is quite slow), the heat is distributed better through water because 1) sunlight penetrates deeper and 2) convection distributes the heat faster in water.