2 Review What is potential energy? Energy at rest or energy due to position
3 What is a conservative force? A conservative force is a force that does work in such a way that the work done depends only upon the initial and final positions.
4 Frictional force is dissipative. The Coulomb force is conservative.
5 What is meant by the conservation of energy? Energy cannot be created or destroyed, only transformed.
6 Gravitational force is conservative. Gravitational potential energy depends upon mass, gravity, and position.
7 Introduction New concepts Electric potential energy Electric potential Voltage between two pointsElectric potential differenceCapacitance
8 Work Done on a Charge Electrostatic force is conservative Work may be done by a conservative force
9 The equation for work done on a charge: Since F = qEW = (F)d = (qE)d
10 Electric Potential Electric potential (V) is a scalar quantity It is defined as the energy per unit charge (J/C) at a given pointThe unit for electric potential is the volt (1 volt = 1 Joule/Coulomb)
11 Potential DifferenceDefinition of the potential difference (DV) between points A and BDV = VB - VA = DPE/q = -E.dThe units are Volts or Joules /Coulomb
13 Electrical PE and KEA positive charge gains electrical PE when it moves against the field.A positive charge gains KE when it moves in the same direction as the field.166, 16.2
14 A negative charge gains KE when it moves against the field. A negative charge gains electrical PE when it moves in the same direction as the field.A negative charge gains KE when it moves against the field.167
15 Potential Difference And Electric Potential A 12-volt automobile batteryMaintains a potential difference across its terminalsThe positive terminal is at a higher potential. (+ 12 volts)The negative terminal is at a lower potential (0 volts) and is connected to the car frame.Charge moves around the circuit.16.3
16 Zero PotentialA point of zero potential is usually defined by grounding some point in the circuit.
17 A point at infinity may be considered to be at zero potential in relation to a positive charge.
18 Electric Potential at a Point The electric potential, at a particular location, created by a point charge can be found by using:V = ke(q/r)
19 Electric PotentialThe electric potential depends upon only two things:
20 The electric potential depends upon only two things: ChargeLocation
21 The electric potential exists at every point surrounding a given charge. A second charge is not needed.
22 Electric potential is a scalar quantity. If there are two or more charges, the potentials add algebraically at a given point.no vectors to worry about
23 Electric PEElectric potential energy is the energy that a charge has due to its position in the electric field produced by another charge. It is measured in Joules.133
24 The electric potential (PE) energy of a pair of charges can be found by using: PE = q2V1 = q2(keq1/r)PE = ke (q1q2/r)16.7
25 The electric potential energy is positive if the charges are identical and negative if they are different.
26 EquipotentialsNo work is required to move a charge between two points that are at the same potential.W = -q(VB – VA)
27 All points on the surface of a charged conductor which is in electrostatic equilibrium are at the same potential.
28 The electric potential is constant everywhere on the surface of a charged conductor in equilibrium.
29 The electric potential is constant everywhere inside a conductor and equal to its value at the surface.
30 The Electron-VoltThe electron-volt is the energy of an electron after it has been accelerated across a potential difference of 1 volt.It is a very small unit of energy.1 eV = 1.6 x J
31 Equipotential Surfaces What is an equipotential surface?An equipotential surface is one where all points are at the same potential.169
32 No work is required to move a charge at a constant speed along an equipotential surface. 134
33 The electric field at every point of an equipotential surface is perpendicular to the surface. 16.7
34 Equipotential Lines Equipotential lines Two-dimensional views Equipotential lines are always perpendicular to electric field lines.16.10, 170, 16.6
35 Applications Electrostatic precipitator Electrostatic air cleaners Power company smokestacksElectrostatic air cleanersFurnace filtersSmoke eaters at party halls
36 How does a copy machine work? CorotronSelenium drumHeated pressure rollers165
39 Capacitors What is a capacitor? A capacitor is made up of two parallel metal plates with a surface area (A) separated by a dielectric with thickness (d)171
40 How it works: 68 Each plate is connected to one side of a battery Charge flows until the plates have the same potential difference as the batteryOne is positive while the other is negative (+ Q and –Q)68
41 The Definition Of Capacitance What is capacitance?Capacitance is the ratio of the magnitude of the charge on either conducting surface to the potential difference between the two conducting surfaces.C = Q/DVTherefore: Q = DV.C
42 What is the unit of capacitance? Farad (F)Named after Michael Faraday1 farad = 1 Coulomb/voltMicrofarads (mF) and picofarads (pF) are more commonly used
43 Capacitance Applications Tuning stations on radio and television receiversStoring charge in electronic flash unitsComputer keyboards
44 The Parallel Plate Capacitor Factors affecting capacitance:Area (A)Separation (d)Permittivity of free space (eo)C = eoA/d (in air)Also: ke = 1/4peo