Electrical Potential Voltage

How can we manipulate energy in electric fields? Apply FORCE to push like charges TOGETHER FA FA + + Apply FORCE to push unlike charges APART FA FA + -

How much electrical PE? Electrical P.E. is also called VOLTAGE or POTENTIAL DIFFERENCE Unit = VOLT 1 Volt = 1 Joule/Coulomb

Example #1 V = W q V = 6 J 3C V = 2 J/C or 2 V An object with +3 coulombs of charge is pushed toward a positively charged plate. 6 joules of energy are expended in pushing the charge. What amount of electrical potential energy has been stored in the field between the charged object and the plate? V = W q V = 6 J 3C V = 2 J/C or 2 V

- - Removing Energy - - - - - - - - - - - Example #2 An object with 2 coulombs of charge is accelerated using an electrical potential of 10 volts. How much kinetic energy does the object receive? Removing Energy This stored energy can also be released. What happens to energy that comes OUT of a field? Transfers into kinetic energy V = W q 10 V = W 2C W = 20 J The field releases the energy, doing WORK on the charge! - - STORING ENERGY - - - - - - - - - - -

Example #3 An object with a charge of 0.5 coulombs is pushed 0.2 meters toward a negatively charged plate with a force of 10 newtons. What is the energy required to do this? W = Fd = (10 N)(0.2 m) = 2 J What is the electrical potential energy of the object after it is pushed? V = W = 2 J = 4 V q 0.5 C

Example #4 An electron travels a distance of 2 x 10-3 m while being raised to an electrical potential of 3000 volts. What is the work done on the electron? V = W / q W = Vq = (3000 V)(1.6 x 10-19 C) = 4.8 x 10-16 J

Electron-volts 2 eV 4 eV 4 eV = 6.4 x 10-19 J 2 eV = 3.2 x 10-19 J The electron-volt (eV) is a unit of ENERGY Electron-volts are a SHORT CUT to finding ENERGY when dealing with FUNDAMENTAL CHARGES. An electron-volt is the amount of energy needed to raise the electrical potential of an electron (or proton) by 1 volt What is the energy needed to raise two electrons to a potential of 1 volt? What is the energy needed to raise two electrons to a potential of 2 volts? 2 eV 4 eV 4 eV = 6.4 x 10-19 J 2 eV = 3.2 x 10-19 J

What use is electrical potential? Higher VOLTAGE We use this by putting a RESISTOR in the path of the ELECTRONS – as they go through the RESISTANCE they do WORK on it! The electrons naturally “want” to drop to a lower energy How do they get there? A battery is a tool that forces electrons to a higher electrical P.E. - gives them VOLTAGE RESISTOR