# Year 9 Heat Transfer Learning Objectives

Students should know and be able to apply the following :

• The higher the thermal conductivity of a material the higher the rate of energy transfer by conduction across the material.
• Students should be able to describe how the rate of cooling of a building is affected by the thickness and thermal conductivity of its walls. Students do not need to know the definition of thermal conductivity.
• The transfer of energy by conduction, convection, evaporation and condensation involves particles and how this transfer takes place.
• The factors that affect the rate of evaporation and condensation.
• All bodies (objects), no matter what temperature, emit and absorb infrared radiation. The hotter the body, the more infrared radiation it radiates in a given time.
• The rate at which an object transfers energy by heating depends on: the surface area, volume and material of the object and the nature of the surface with which the object is in contact.
• The bigger the temperature difference between a body and its surroundings, the faster the rate at which heat is transferred.
• A perfect black body is an object that absorbs all of the radiation incident on it. A black body does not reflect or transmit any radiation.
• Since a good absorber is also a good emitter, a perfect black body would be the best possible emitter.
• Students should be able to explain:
• that all bodies (objects) emit radiation
• that the intensity and wavelength distribution of any emission depends on the temperature of the body.
• A body at constant temperature is absorbing radiation at the same rate as it is emitting radiation.
• The temperature of a body increases when the body absorbs radiation faster than it emits radiation.
• The temperature of the Earth depends on many factors including: the rates of absorption and emission of radiation, reflection of radiation into space.
• Students should be able to explain how the temperature of a body is related to the balance between incoming radiation absorbed and radiation emitted, using everyday examples to illustrate this balance, and the example of the factors which determine the temperature of the Earth.
• Students should be able to use information, or draw/interpret diagrams to show how radiation affects the temperature of the Earth’s surface and atmosphere.