Electrical Potential Voltage How can we manipulate energy

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 -

Electric Fields • The electric field can store energy. Charges gain potential energy when moved against the field in the same way as masses gain energy when lifted against gravity. • The electric field can do work! (remember the work/energy connection) when they move charges. Work done against the field to move the charge equals PE or KE gained by the charge

Electrical Potential Energy a. In an elevated position, the ram has gravitational potential energy. When released, this energy is transferred to the pile below.

Electrical Potential Energy a. In an elevated position, the ram has gravitational potential energy. When released, this energy is transferred to the pile below. b. Similar energy transfer occurs for electric charges.

Electrical Potential Energy • The energy a charge has due to its location in an electric field is called electrical potential energy.

Electric Potential • If we push a single charge against an electric field, we do a certain amount of work. • If we push two charges against the same field, we do twice as much work. • Two charges in the same location in an electric field will have twice the electrical potential energy as one; ten charges will have ten times the potential energy. • It is convenient when working with electricity to consider the electrical potential energy per charge.

Electric Potential The electrical potential energy per charge is the total electrical potential energy divided by the amount of charge. At any location, the potential energy per charge—whatever the amount of charge—will be the same. The concept of electrical potential energy per charge has the name, electric potential.

Electrical Potential • Electrical Potential is also called VOLTAGE or ELECTRICAL POTENIAL DIFFERENCE, or POTENTIAL DIFFERENCE • Unit for electrical potential VOLT • 1 Volt = 1 Joule/Coulomb 1 V = 1 J/C Amount of work done in moving a charge and the amount of charge moved

Example #1 6. 0 joules of work are done pushing an object with 3. 0 coulombs of charge toward a charged plate. • How much electrical potential energy was stored in the electric fields? 6. 0 J • What is the electrical potential difference in the field between the charged object and the plate? V = W/q V = 6. 0 J / 3. 0 C V = 2. 0 V

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

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 potential difference between the object and the plate after it is pushed? V= W = 2 J =4 V q 0. 5 C

Example #4 An electron is raised through a potential difference 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 The electron-volt (e. V) is an alternate unit of ENERGY. Electron-volts are a SHORT CUT to finding ENERGY when dealing with ELEMENTARY CHARGES. An electron-volt is the amount ofto energy What is the energy needed toelectrons raiseto 1 elementary charge neededraise to raise a potential ofvolts? 1 volt? two electrons a to potential of 2. 5 through a potential difference of 1 volt. W=q. V = 2 e x 1 V 2. 5 V ==25 e. V 2 5 e. V = 3. 2 8. 0 x 10 -19 J

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