Exam 1 Review

Exam 1 Review - Lesson 1 Breakfast -appliances either heat...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
Lesson 1 Breakfast -appliances either heat or work -3 types of heat transfer: Conduction: pass heat to another layer; The atoms will be fixed in their relative positions but as they heat up they will vibrate more and pass along some of that energy Radiation: It is electromagnetic radiation and it does not need a medium to propagate Convection: movement of currents in fluids; the molecules are moving around and have collisions, and will keep on colliding until there is a distribution of energy. The Refrigerator -Fridge is an example of a ‘heat pump’ a device that moves heat. The casing is simply an insulated box, so the heat can not get in; at the back there is a heat exchanger, a coil where the heat from inside the refrigerator can be dissipated -The refrigerant will be a liquid with a low boiling point. Thus, we can convert refrigerant from the liquid phase into the gas phase easily. This needs a lot of energy, but we have the heat in the fridge. By pumping in the liquid refrigerant and allowing it to expand and form a gas will cool the inside; then we can pump it through the coils and exchange the heat with the room. Unfortunately the gas is not at a very high temperature and so the heat exchange does not work well, UNLESS we concentrate the heat in the gas, which we can do with the compressor . This will compress (pressurize) the gas so the heat is concentrated and thus the heat exchange will be more efficient and the coils at the back of the refrigerator will be enough to cool the gas down so it will turn back into a liquid and the process can be repeated Lighting -Efficiency = useful energy out/ energy X 100 -before crude oil was found, people used sperm whale oil. Kerosene can be produced and used as a clean burning light source. -Light bulbs Incandescent: the filament gets so hot –white hot—that it produces a light; they produce a lot of heat; they are only 5% efficient. Fluorescent: electrodes inside the tube excite mercury and gives off UV radiation which excites a phosphate on the inside of the bulb that gives off light. Halogen lights: they produce a lot of heat and a lot of light; they are expensive to use; they are used for outdoor security lighting, headlights on cars, and sporting event lighting Compact Fluorescent Lights: The incandescent light bulb produces light by heating a tungsten wire to white hot temperatures Home Heating -in the NE, about 44% of our electricity bill is for heating & cooling -we can save energy if we keep heat inside in the winter and out in the summer insulation -air escapes mostly thru floors, walls, and ceilings (31%); then ducts (15%); then fireplace (14%); then doors (11%); then windows (10%) -natural gas is popular b/c it usually has low costs and is easy to use; but not all houses have access to natural gas lines—these houses will use electricity or oil -burning wood: The solar energy is stored in the plant in the form of chemical energy which is released as thermal energy during the combustion process. Geothermal Heating/ Cooling
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 7

Exam 1 Review - Lesson 1 Breakfast -appliances either heat...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online