Lab 4, 5, 6 Studyguide
Lab 4, 5, 6 Studyguide SCI 1101
Popular in Science, Society & Environ I
verified elite notetaker
Popular in Department
This 3 page Study Guide was uploaded by nako.nako.nako on Tuesday October 4, 2016. The Study Guide belongs to SCI 1101 at Kennesaw State University taught by Professor Kay Abikoye in Fall 2016. Since its upload, it has received 51 views.
Reviews for Lab 4, 5, 6 Studyguide
Report this Material
What is Karma?
Karma is the currency of StudySoup.
You can buy or earn more Karma at anytime and redeem it for class notes, study guides, flashcards, and more!
Date Created: 10/04/16
Lab 4 First Law of Thermodynamics (aka “Conservation of Energy Principle”) - Energy can neither be created nor destroyed; it can only be TRANSFERRED from one from to another - ∆E = W + Q ∆E = change in the energy of an object W = work done on the object, Q = heat added to an object. Joule - The English scientist James Joule found that the heat and work are equivalent methods for changing the energy of an object. 2 2 - 1J = 1kg m /sec Heat - the energy transferred between objects of different temperature. - Once heat enters an object, it increases the internal energy of an object, which is the same result that doing work on the object would produce. The object does not contain the heat or the work; it merely changes its energy because of them. Temperature - the property that two objects have in common when no heat is transferred between them when placed in thermal contact. - Ex) Measure the temperature of a glass of water with a mercury or alcohol thermometer. During this time, heat is being exchanged between the water and the liquid in the thermometer. As it does so, the temperature of the liquid in the thermometer changes, becoming closer to that of the water. This change in temperature of the alcohol or mercury results in its volume changing, which is what changes the level of the fluid in the thermometer. - The only thing that is being measured is the VOLUME of the liquid in the thermometer. Conduction - occurs when two regions of different temperature are put into direct contact, but are not allowed to mix. - The most predominant type of heat transfer for the majority of homes - The rate at which heat gets transferred depends upon - the rate of heat transfer = A k (T T ) / L H C - (1) the thickness of the material L - (2) the thermal conductivity k (this depends on the composition of the material) - (3) surface area of the material A, and - (4) the temperature difference between the reservoirs. (THT C) - Rvalue - thickness/thermal conductivity = l←thickness k←thermalconductivity 2 o - the common units: ft hr F/Btu - R T sum of all of the individual Rvalues - conductive heat transfer through a single substance rate of heat transfer = A (H C ) k/L = A (T H C)/R - conductive heat transfer through multiple substances rate of heat transfer = A (H C )/R T R = sum of all of the individual Rvalues T Lab 5 Conduction - occurs when two regions of different temperature are put into direct contact, but are not allowed to mix. - Ex) Temperature between outside of wall and inside the wall. Convection - heat transport by movement and mixing - Ex) When we open the doors to our homes, hot and cold air are allowed to mix, and heat is convected. - Ex) occurs through cracks or breaks in our windows, walls, doors, ceilings, and floors. - The number of air exchanges per hour is a measure how much energy you will need to use in order to counter the effects of heat transfer via convection. Second law of Thermodynamics - the total amount of usable energy that comes out of any process will be less than the total amount of energy that went into the process. (No energy transfer can ever be 100% efficient) "Heat will flow spontaneously from hot to cold", "", "A heat engine and a heat pump both require a hot and a cold reservoir" “In a closed system, the total entropy either increases or stays the same” Entropy is the logarithm of the number of states accessible to a system (1/T = (dS/dU)N) T = temperature; S = entropy; U = total energy of the system - waste heat = between the total amount of energy input the usable energy output - efficiency = a measure of the amount of usable energy that is generated during any type of transfer - If transfer is more efficient, total usable energy will be closer to the original usable energy. - Ex) the 5% efficiency of an incandescent light bulb < the 20% efficiency of an fluorescent light bulb - all of the transfers need to be in consideration when measuring efficiency - ex) When measuring the efficiency of a car, these factors of transfer has to be taken in to account: efficiency of the electric motor, efficiency of the internal combustion engine, types of transmission systems, gasoline, etc Energy Use in the Home - The amount of money consumed by an appliance depends on: type of fuel, power of the appliance, and the length of the time - Ex) average electric oven uses an average of about 2,000 watts of power to heat itself to a temperature of 350 o F. If it is run for 1 hour, then it will use an amount of energy equal to… Energy = Power x Time = 2000 watts x 1 hour = 2000 watthour = 2 kilowatthour - Ex) The average natural gas stove uses about 11,000 Btu/hr to maintain the same temperature. If you ran it for the same amount of time as the electric stove, it would consume an amount of energy equal to Energy = Power x Time = 11000 Btu/hr x 1 hour = 11000 Btu - Cost of appliances: Power x Time x Cost of Electricity Lab 6 The amount of money that you would spend in making the change divided by the amount of money you would save each year will tell you how many years it would approximately take to pay off your investment. Scenario 1: Savings/year = $ 20 Description of change: single pane windows replaced by double pane windows. Cost = $100 Payback time = 5 years 100 dollars for a double paned window / 20 dollars saved per year = 5 years to pay off investment. Scenario 2: Savings/year = $ 50 Description of change: installing more energy efficient doors Cost = $200 Payback time = 4 years 200 dollars for new energy efficient doors / 50 dollars saved per year = 4 years to pay off investment.
Are you sure you want to buy this material for
You're already Subscribed!
Looks like you've already subscribed to StudySoup, you won't need to purchase another subscription to get this material. To access this material simply click 'View Full Document'