Energy, Temperature and Heat

Transcription

1 Energy, Temperature and Heat Some loose definitions: Energy: The capacity to do work (or loosely, the potential to make something happen) Energy can be transferred in the form of heat or radiation (among other processes) Power: The rate at which energy is transferred from one object to another (i.e., the energy per unit time) Temperature: A measure of the energy associated with the motion and vibration of an object's molecules (loosely, a measure of the stored heat energy) Heat: The energy transferred between objects because of differences in temperature

2 Specific Heat Given a gram of some substance, the amount of heat needed to raise the temperature by 1 o C is the material's specific heat. Two ways you might look at this: An object with higher specific heat requires more heat to be added to produce a given change in temperature. Or stated a different way... For a fixed amount of heat added, an object with higher specific heat has a smaller temperature change.

3 Specific Heat Given a gram of some substance, the amount of heat needed to raise the temperature by 1 o C is the material's specific heat. Two ways you might look at this: Notable fact: the specific heat of water is roughly 2 to 5 times greater than the specific heat of land. heat from sun

4 Specific Heat Given a gram of some substance, the amount of heat needed to raise the temperature by 1 o C is the material's specific heat. Two ways you might look at this: Notable fact: the specific heat of water is roughly 2 to 5 times greater than the specific heat of land. heat from sun low specific heat, bigger temperature change high specific heat, smaller temperature change

5 The difference in the specific heats of land and water is responsible for the sea breeze. During the day, the cooler, heavier air over the water undercuts the warmer, lighter air over land The boundary where the cooler and warmer air meet is called the sea breeze front warmer air cooler air sea breeze front

6 The difference in the specific heats of land and water is responsible for the sea breeze. During the day, the cooler, heavier air over the water undercuts the warmer, lighter air over land The boundary where the cooler and warmer air meet is called the sea breeze front lake breezes over Michigan

7 The difference in the specific heats of land and water is responsible for the sea breeze. During the day, the cooler, heavier air over the water undercuts the warmer, lighter air over land The boundary where the cooler and warmer air meet is called the sea breeze front rising air at the sea breeze front often leads to thunderstorms

8 Radiation: Basic Concepts Radiation refers to energy transmitted by electromagnetic waves (or waves of electric and magnetic force) Radiation differs from heat in that it travels from emitter to absorber without affecting the intervening space Earth absorber Sun emitter no effect on intervening space

9 Radiation: Basic Concepts Radiation refers to energy transmitted by electromagnetic waves (or waves of electric and magnetic force) Radiation differs from heat in that it travels from emitter to absorber without affecting the intervening space Radiation is classified by its wavelength (or peak-to-peak distance), often denoted by λ - Typical units range from micrometers ( m) to meters (m), with λ 1 m = 10-6 m

10 electromagnetic waves classified by wavelength

11 Category Wavelength TV, radio microwave infrared (IR) visible ultraviolet gamma-ray, X-ray ~ 1 to 100 m ~ 0.1 to 1 cm ~ 1 to 100 m ~ 0.4 to 0.7 m ~ 0.1 m < 0.1 m electromagnetic waves classified by wavelength

12 Category Wavelength TV, radio microwave infrared (IR) visible ultraviolet gamma-ray, X-ray ~ 1 to 100 m ~ 0.1 to 1 cm ~ 1 to 100 m ~ 0.4 to 0.7 m ~ 0.1 m < 0.1 m electromagnetic waves classified by wavelength

13 All substances continuously emit and absorb radiation The wavelengths emitted / absorbed depend on both the temperature and properties of the object's surface Emission and absorption are characterized in terms of

14 All substances continuously emit and absorb radiation The wavelengths emitted / absorbed depend on both the temperature and properties of the object's surface Emission and absorption are characterized in terms of Emission spectrum: The energy emitted by an object as a function of wavelength the emission spectrum of the sun

15 All substances continuously emit and absorb radiation The wavelengths emitted / absorbed depend on both the temperature and properties of the object's surface Emission and absorption are characterized in terms of Absorption spectrum: The fraction (or percentage) of incident energy absorbed by an object as a function of the wavelength the absorption spectrum of CO 2