Heat can be transferred by Conduction Convection Advection

Heat can be transferred by: • Conduction • Convection • Advection • Radiation www. soran. edu. iq

Our atmosphere has a several gases that are selective absorbers of radiation. These gases include: • • • Water vapor (H 2 O) Carbon Dioxide (CO 2) Nitrous Oxide (N 2 O) Methane (CH 4) Ozone (O 3) • These gases are good absorbers and emitters of Infrared Radiation (IR). They absorb the IR emitted from the surface of the Earth and gain kinetic energy, the excited gas molecules collide with other molecules and increasing the temperature of the air. • Example Greenhouse www. soran. edu. iq

How does Earth's atmosphere deal with solar radiation? Describe what is going on and how each method of heat transfer works in this example: www. soran. edu. iq

Heat Transfer on Earth • • • How is the Earth's surface heated? How is the atmosphere heated? How is heat lost into space? www. soran. edu. iq

Heat Transfer on Earth ü How is the Earth's surface heated? • • How is the atmosphere heated? How is heat lost into space? Heating Earth's surface The Earth's surface can be considered both the land surface and the surface of the oceans and lakes. Heat from core The core of the Earth is very hot. The thermal energy of that core is transferred to the surface of the Earth and lower levels of the oceans by conduction. Water in lakes and oceans transfers heat to the surface by convection. Effect of conduction of heat from the core is not really significant, as can be seen in winter months. Heat from Sun Electromagnetic radiation from the Sun is absorbed by the soil and bodies of water, thus heating them. This is especially true when the angle of the sunlight is fairly perpendicular to the ground, as in the summer months. In wintertime, the radiation from the Sun comes in at an angle and is not as readily absorbed. Also the days are shorter and often cloudy, so less sunlight hits the ground. Another factor is when there is snow on the ground, most of the sunlight is reflected back into space. www. soran. edu. iq

Heat Transfer on Earth Heat from core The core of the Earth is very hot. The thermal energy of that core is transferred to the surface of the Earth and lower levels of the oceans by conduction. Water in lakes and oceans transfers heat to the surface by convection. Effect of conduction of heat from the core is not really significant, as can be seen in winter months. www. soran. edu. iq

Heat Transfer on Earth • ü • How is the Earth's surface heated? How is the atmosphere heated? How is heat lost into space? Heating the atmosphere The atmosphere is heated by electromagnetic radiation from the Sun, conduction from contact with warm land water, convection to even out the temperature and by absorption of infrared radiation from the warm land water. Radiation from Sun Most of the electromagnetic radiation coming from the Sun passes right through the atmosphere, because the wavelength of visible light is not readily absorbed in air. The infrared portion of sunlight is absorbed, thus heating the air. Convection then spreads and evens out the heat. Contact with land water Air molecules that come into contact with the warmer land surface of the oceans and lakes increase their thermal energy through conduction. Those molecules then heat up other air molecules through convection. In the winter, the land water is cold, thus cooling the air. www. soran. edu. iq

Absorption of infrared radiation • When land water become warm, the materials emit long-wavelength infrared radiation that is readily absorbed by the atmosphere. This even happens at nighttime. Convection in the air then spreads out thermal energy throughout the atmosphere. Of course, the ground and water are cold in winter and thus do not emit infrared radiation to heat the air. www. soran. edu. iq

Heat Transfer on Earth • • ü How is the Earth's surface heated? How is the atmosphere heated? How is heat lost into space? www. soran. edu. iq

Heat loss and equilibrium • The warm surfaces of land water radiate infrared energy. Most of it passes through the atmosphere and is lost in outer space. Some of that energy is absorbed in the atmosphere, thus heating it. Under normal conditions, the amount of thermal energy heating the Earth and its atmosphere from core heat and radiation from the Sun is the same as the amount lost into space in the form of infrared radiation. • Thus the Earth's average temperature stays relatively constant, and there is equilibrium between input heat and heat lost. www. soran. edu. iq

Excess of gases cause global warming • The present situation is that there has been an increase in infrared-absorbing gases in the atmosphere, such as carbon dioxide (CO 2) and methane (CH 4). Energy that would normally escape into space is absorbed by these molecules, thus heating the atmosphere and spreading through convection currents. The average temperature of the atmosphere has increased 0. 25 °C since 1980, mainly attributed to an increase in infrared-absorbing gases in the atmosphere. • Heat from the Earth's core and radiation from the Sun is transferred to the surface of the Earth by conduction. Contact of the atmosphere with these warm surfaces transfers thermal energy, which then heats up the rest of the air through convection. • The atmosphere is also slightly heated by absorption of electromagnetic radiation from the Sun. The warm land water radiates infrared, some of which is absorbed by the atmosphere, adding to its thermal energy. The remaining heat on the surface is sent out into space in the form of infrared radiation. www. soran. edu. iq

• Solved Example : Aluminum has a specific heat of 0. 902 J/g x o. C. How much heat is lost when a piece of aluminum with a mass of 23. 984 g cools from a temperature of 415. 0 o. C to a temperature of 22. 0 o. C? Answer Step 1: First read the question and try to understand what they are asking you. Can you picture a piece of aluminum foil that is taken out of an oven. Imagine the aluminum losing heat to its surroundings until the temperature goes from 415. 0 o. C to 22. 0 o. C. Step 2: Write the original formula. q = m(d. T)Cp Step 3: List the known and unknown factors. Looking at the units in the word problem will help you determine which is which. q=? m = 23. 984 g T = (415. 0 o. C - 22. 0 o. C) = 393. 0 o. C Cp = 0. 902 J/g x o. C (remember, they asked for the change in temperature) Step 5. Cross out units where possible, and solve for unknown. Step 6. Round to the correct number of significant digits and check to see that you answer makes sense. www. soran. edu. iq

Homework www. soran. edu. iq