Egee 101 Lesson 1 The first heat transfer mode to the kettle is conduction The metal of the kettle is in contact with the metal of the heating element and heat always flows from hot to cold so there is heat transfer Radiative heat transfer is how the warmth of the sun is transferred to you when you re out or how you warm your hands in front of the fire It is electromagnetic radiation and it does not need a medium to propagate Thus it can travel through space The water molecules are free to roam about as they are not fixed in relative positions unless frozen like the metal atoms So as a water molecule heats up it has more energy and travels further The molecules moving around have lots of collisions think bumper cars but this molecular billiards occurs without energy loss heat pump a device that moves heat electricity which is used to heat a tungsten filament The thin metal strand the filament gets so hot it becomes white hot producing a nice white light incandescent light bulb is also inefficient 5 efficient Efficiency Useful energy out energy in x 100 We measure the flow of electricity by the term Watt W Flourecent far more efficient x 4 incandescent so around 20 Offices universities malls supermarkets apartment complexes will all use this type of lighting as the light is on for long time periods often 24 hours a day in some locations the local WalMart for example LED s are small light sources that become illuminated by the movement of electrons through a semiconductor material link is external they are increasingly common in general lighting and have a nicer color than compact fluorescent lighting They are also being used in traffic lights streetlights xmas tree lights and other more common applications flashlight halogen these are very inefficient and it might surprise you to learn they cost an average of 300 a year to run normal use I used to have one but threw it away Halogen lights do have their uses however exterior security lighting sporting event lighting headlights in your car for those driving the nicer cars anyway The halogen gas in the bulb helps keep the filament insulated so it loses less heat Cfl Fluorescent is a lot better at about 20 efficient converting electricity into light bout 44 of the utility bill is heating cooling heating degree days HDD for our heating needs and the summer equivalent cooling degree days CDD We use R values to measure the insulating property of the material the resistance of an area of material to heat flow over time The units are h hours ft2 is area F is degrees F and Btu is energy British thermal units So as that is a mouthful we just report the R value without the units h x ft2 x F Btu the higher the R value the better the insulating ability We can increase the R value by adding more thickness insulation or by changing the insulating material to a higher R value biomass combustion burning wood How does a microwave oven operate A Microwave TM Is Just A Brand Name Of Toaster Oven B Microwaves Heat A Pool Of Water Which Steams The Food hence the steam that comes off food fresh out of the microwave C Microwaves Penetrate The Food And Excite The Internal Water Molecules Feedback Correct A microwave oven operates by bombarding your food with micro waves These waves excite the food molecules particularly the water molecules in the food giving them more movement and energy An increase in molecular movement and energy is equal to an increase in temperature Microwaves can also be used as a secure communication device D Microwaves Heat A Filament Which Produces Heat Table for Individual Question Feedback Points Earned 5 0 5 0 2 Electricity generated from a coal fired power plant costs approximately 4 per kW hr Electricity generated from a farm of wind turbines costs approximately 9 per kW hr If a household chooses to purchase renewable electricity generated from the wind how much more will it cost the family Assume the during one year then family consumes 10 000 kW hrs of electricity A 900 B 1300 C 500 Feedback Correct The difference in price between the two choices is 5 cents 9 cents minus 4 cents Over 104kW hrs of electricity the cost will be 104kW hrs 0 05 500 D 400 Table for Individual Question Feedback Points Earned 5 0 5 0 3 When a refrigerant changes phase from a liquid to a gas what does it do A It Adsorbs Heat Feedback Correct Expansion of a fluid from the liquid phase to the gas phase absorbs A LOT of heat Think about how much heat is required to boil water Similar to sweating where the water evaporates thus cooling you Note this is not water to steam B It Makes A Whistling Sound C It Creates Energy D It Gives Off Heat Table for Individual Question Feedback Points Earned 5 0 5 0 4 Of the following which allows the greatest amount of air to flow into a home A Doors B Windows C Fire Places Feedback Correct Fireplaces contribute to 14 of the total air infiltration into a home Besides keeping the flue closed when not in use there is little one can do to prevent air from entering through the fireplace DOE D Electric Outlets Table for Individual Question Feedback Points Earned 5 0 5 0 Source 5 In TA s apartment the monthly electric bill is 60 one wonders If electricity totals a cost of 6 6 per kilowatt hour including all the fees such as line charges transfer fees generation fees etc approximately how many kilowatt hours of electricity does a typical student apartment consume in a month A 1500 kW hr B 900 kW hr Feedback Correct 60 0 066 per kW hr 909 kW hrs C 200 kW hr D 500 kW hr Table for Individual Question Feedback Points Earned 5 0 5 0 6 In the Northern Hemisphere which direction should a home face to receive maximum benefits from solar radiation A West B North C South Feedback In the northern hemisphere where the United States is located a home should face due south to receive the maximum exposure to solar energy This is hard to do because typically homes face the road no matter what direction it may be So a home that will take advantage of solar energy may take some planning D East Table for Individual Question Feedback Points Earned 5 0 5 0 7 Which types of plants are best to plant around your home in order to keep sunlight out during summer months but allow sunlight in during winter months A Various Shrubs B Pine Trees C Deciduous Trees Feedback Correct Deciduous trees are the best choice for maximizing the benefits of solar radiation In the summer months these trees are full of foliage that provides shade from the rays thus