Electric Fields, Electric Potential Energy & Electric Field Intensity

A charged object is any object in which there is an imbalance of electrical charges (there are more electrons than protons or more protons than electrons). An electric field: is invisible and found around (in 3-dimensions) a charged object is a vector quantity (it has magnitude and direction) has a direction that a proton would move in if the proton were placed in the field. The field lines point toward negative charges & away from positive ones has a magnitude that is the force in newtons per coulomb of charge obeys the inverse-square law. Electric Fields - +

Field lines: Are used to indicate the direction of electric fields. An arrow on the end opposite the more positive area. They show how strong the field is: Many field lines, close together indicates a strong field. Only a few lines, far apart, indicate a weak field. Fields exist around single points or even from one flat or curved plate toward another plate. Electric Fields

Electric potential energy is energy that a charged object has due to its location in an electric field. The stronger the field, the greater the electric potential energy. The greater the charge, the greater the electric potential energy. In the same electric field, a pair of electrons would have twice the electric potential as a single electron. In a field with strength 10 newtons per coulomb (10 N/C), an electron would have twice the electric potential energy as it would in a field of strength 5 N/C. Electric Fields

Draw the field lines between the proton on the left and the electron on the right… +-

Draw the field lines between the proton on the left and the proton on the right… + +

If a charge is to move with an electric field, the field does work on the charge. If the charge is to move against the field, work must be done on the charge. This is somewhat like a toy dart gun. To give the gun/dart system some elastic potential energy, some work must be done in pushing the dart against the spring inside the gun. When the dart is released, the spring does work on the dart, changing electric potential energy, EPE, into kinetic energy, KE. Electric Fields

In the following slide, the field direction is from left to right… That means that a positive charge placed in the field would be pushed to the right by the field (the field does the work on the positive charge)… It also means that moving a positive charge to the left would require work from an outside source. Electric Fields

Electric Potential Energy: It requires work to push a charged particle against the electric field… increases Note how the EPE increases as the positive charge is pushed against the field…+ + Electric Fields Electric Potential Energy Monitor

A released particle accelerates away from the sphere as electric PE is changed to KE… decreases Note how the EPE decreases as the positive charge is pushed by the field. + Electric Fields Electric Potential Energy Monitor

Electric Potential Energy Batteries and generators pull negative charges away from positive ones, doing work to overcome electrical attraction. The amount of work depends on number of charges and separation distance. Work done by a battery or generator is then available to a circuit as electrical PE. Electric Potential Energy

Electric potential is electric potential energy per charge; the energy that a source provides to each unit of charge: Electric potential = electric potential energy charge W V =  Q (OR) W = VQ (OR) Q = V/W Units: V = joules/coulomb, W = joules, Q = coulombs. Electric Potential

Electric potential and voltage are the same. volt The unit of measurement is the volt… How much work is done when a 9 volt battery moves 2 coulombs of charge through it? Energy = Work = Voltage x Current… W = VQ W = (9 v)(2 C) W = (9 J/C)(2 C) W = 18 J Electric Potential

How much charge can be moved through a potential difference of 36 volts using 9 joules of work? W = VQ Q = W/V Q = (9 J)/(36 V) Q = (9 J)/(36 J/C) Q = 0.25 C Electric Potential

How much work can be done by a charge of 6 coulombs if it has 12 volts of electric potential as a source of energy? W = VQ W = (12 V)(6 C) W = (12 J/C)(6 C) W = 72 joules