conversion & conservation of energy living with the lab © David Hall 2013 windmill pumping water for cows – west Texas
living with the lab 2 fossil fuels coal fired power plant in Arizona pumpjacks in West Texas HOW IT WORKS: chemical reaction (combustion) creates heat make steam and/or hot exhaust gases steam or exhaust gas turns turbine turning turbine makes electricity burning of natural gas:
living with the lab 3 wind power HOW IT WORKS: wind causes turbine to turn turning turbine generates electricity wind turbines in California
living with the lab 4 solar energy HOW PHOTOVOLTAIC CELLS WORK: sun strikes a semiconductor material electrons gain energy resulting in a buildup of voltage between electrodes this voltage is harnessed to produce electric power solar farm in Arizona
living with the lab 5 hydroelectricity Hoover Dam – Colorado River – Lake Mead HOW IT WORKS: water behind dam creates a large pressure differential across turbine moving water contacts turbine blades, forcing them to turn turning turbine generates electricity
living with the lab 6 nuclear energy morgueFile: HOW IT WORKS: splitting atoms creates heat heat creates steam steam turns turbine turning turbine makes electricity
living with the lab 7 conservation of energy Energy can change form, but it can’t be created or destroyed. For our fishtank system, we will run electricity through a resistor to create heat to increase the temperature of water... Within an isolated system, energy is constant.... converting electrical energy into thermal energy resistor - +
living with the lab 8 first law of thermodynamics change in energies: internal energy change (temperature) kinetic energy change potential energy change energy coming in and going out of system: heat transferred to or from a system work done to or by a system The first law is often written as follows:
living with the lab 9 (we assume no heat is lost by conduction through the wall of the pipe or at the surface of the water) (we assume that nothing is moving) the “system” here is defined by the boundary of the water the heater, PVC and air above water are NOT part of our system we apply the first law only to our system, carefully accounting for all energy crossing the system boundary our application of the first law - +
living with the lab 10 our application of the first law zero since our system doesn’t make anything move heat transfer from heater change in energy of water due to temperature change
living with the lab 11 what is heat capacity??? ⁰C 1 kilogram of water
12 living with the lab morgueFile:
living with the lab