HEAT TRANSFER

HEAT Heat is the movement of thermal energy from a substance at a higher temperature to another at a lower temperature. Thermal Energy- the total energy of all the particles in a substance.

How is heat transferred? There are 3 ways that heat can move: Conduction, Convection & Radiation

Conduction In conduction, heat is transferred from one object to another by contact. The particles in the first object are hot and moving fast. When they touch a second object, they bump into those objects causing them to move faster. Conduction mostly occurs in solids.

Examples of conduction

Convection In convection, heat is transferred by the movement of currents within a fluid. A fluid is a liquid or gas. When particles in a fluid get hot, they start moving around faster and spreading apart. When they spread apart they get less dense causing them to rise up.

Convection In convection, hot fluids rise and cold fluids sink. This creates a cycle called a convection current.

Examples of Convection

Radiation In radiation, heat is transferred across a distance. Heat moves in electromagnetic waves from the source of the heat outward. Radiation does not require matter to travel through!

Examples of Radiation

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HEAT MOVES ONE WAY If 2 substances have different temperatures, heat will flow from the warmer object to the colder one. Heat will flow into the other substance until the 2 substances have the same temperature. 100o 50o

Substances that transfer heat easily Conductor- a material that conducts heat well. In other words, a conductor is a material that passes heat along easily because its molecules are very close together. Metal is a good conductor.

Substances that Block heat from transferring Insulator- a material that does not conduct heat well. In other words, an insulator is a material that does not pass heat along easily because its molecules are not very close together. Wood, cloth, paper, cork and rubber are good insulators.

Heating A substance Different substances heat up at different rates. In other words, some substances require more heat to heat up than others. The amount of heat required to raise the temperature of a substance depends on what its made up of. Different materials need more or less heat to change their temperature by the same amount.

Specific Heat Specific Heat is the amount of energy required to raise the temperature of 1 kilogram of a substance by 1 degree kelvin. Scientists have noted the specific heat of several common substances.

change in Heat energy The amount of heat energy needed to change a substance’s temperature depends on several factors: 1. The amount the temperature changes 2. The mass of the substance 3. The specific heat for that substance

Calculating the change in Heat energy We can calculate the change in heat energy by using the following formula: Heat= mass x specific heat x change in temp Q= mc T

Q= 10 x 235 x 14 Q= 32900.0 Q= mc T Q= 32900.0 calories Try this… How much heat is gained by 10kg of silver with a specific heat of 235, if its heated from 21o to 35oC? Q= 10 x 235 x 14 Q= 32900.0 Q= 32900.0 calories c T 35-21= 14 Q= mc T The unit for energy!

You try… m How much heat is lost by 25g of copper if it is cooled from 25o to 5oC? Q= 25 x 0.09 x 20 Q= 45.0 Q= 45.0 cal T 25-5= 20 Q= mc T c