Electrostatics the study of electrical charges at rest Electrodynamics the study of electrical charges in motion opposite Two opposite types of charge exist, named positivenegativeBenjamin Franklin positive and negative by Benjamin Franklin.Benjamin Franklin Benjamin Franklin Charge is a property of matter. Charged particles exist in atoms. Electrons are responsible for negative charge; protons for positive charge; neutrons have no charge. Small amounts of ordinary matter contain incredible amounts of subatomic particles! Conductor material that allows charges to move about easily Insulator material through which charges will not easily move Basic Law of Electrostatics Like charges repel; unlike charges attract Link link rodelectroscope charging a rod and electroscope positivelynegatively positively and negatively conduction induction by conduction and induction conduction When charging by conduction, touches the rod touches the electroscope. same charge The electroscope gets the same charge as the rod. induction does not When charging by induction, the rod does not touch touch the electroscope. The electroscope gets opposite charge the opposite charge of the rod. The direction of the electric field at any point is defined to be the same direction as the direction of force on a positive test charge placed in the region at that point. Field lines point away from positive and toward negative charges. Click here to view a simulation here showing the magnitude and direction of the electric force on a test charge when placed near other charges. Click here to view a simulation of a here charged particle moving through a region occupied by other charges. Electric Potential Difference the change in electric potential energy per unit charge V = W/QV = W/Q The SI unit of electric potential VOLT difference is the VOLT, named in Alessandro Volta Alessandro Volta honor of Alessandro Volta. Alessandro Volta One VOLT is the electric potential difference between two points when one Joule of work is done in moving one Coulomb of charge between the points. the flow of charged particles charged particles ; can be positive or negative, but usually negative (electrons) through a conducting metal Electric current is measured in Amperes, in honor of Andre Marie Ampere Andre Marie Ampere Andre Marie Ampere Andre Marie Ampere. One Ampere is the flow of one Coulomb of charge per second. 1 Amp = 1 Coulomb per second = 1 C/s 1 Amp = 1 Coulomb per second = 1 C/s IQt I = Q/t Ammeter a device that measures current Voltmeter a device that measures electric potential difference Resistance determines the amount of current flow = the ratio of potential difference to current = the ratio of potential difference to current R= V I The SI unit of resistance is the Ohm Ohm, , named Georg Simon Ohm Georg Simon Ohm in honor of Georg Simon Ohm.Georg Simon Ohm One Ohm One Ohm of resistance is the resistance one Volt such that one Volt of potential difference one Amp is needed to obtain a current of one Amp. The resistance of a circuit element depends on: the length of the conductor 1. the length of the conductor as length increases, resistance increases proportionally the cross-sectional area of the conductor 2. the cross-sectional area of the conductor as area increases, resistance decreases proportionally the resistivity of the conductor 3. the resistivity of the conductor as resistivity increases, resistance increases proportionally Ohms Law The ratio of potential difference to current is constant. If R = V/I is a constant value for a given resistor, then that resistor is said to obey Ohms Law. Click here and here to link to pages describing resistor here color codes. Click here and here to run here simulations of Ohms Law. Many circuit elements do not obey Ohms Law. Resistors that get hot, like light bulbs and heating elements, do not keep a constant resistance. Resistance generally increases as objects become hotter. Resistor Circuits Series 1. total resistance is the sum of the separate resistors separate resistors R T = R 1 + R 2 + R current is the same through each resistor I T = I 1 = I 2 = I 3 = total potential difference is the sum of each V T = V 1 + V 2 + V In other words, in a series circuit, resistance and voltage add, but current stays the same. R1R1R1R1 R2R2R2R2 R3R3R3R3 E = 12 V RT =RT =RT =RT = VT =VT =VT =VT = IT =IT =IT =IT = R1R1R1R1 R2R2R2R2 R3R3R3R3 V,V PT =PT =PT =PT = R,I,A P,W R1R1R1R1 R2R2R2R2 R3R3R3R3 E = 12 V R T = 15 V T = 12 V I T = 0.80 A R1R1R1R1 R2R2R2R2 R3R3R3R3 V,V P T = 9.6 W R,I,A P,W Parallel 1. reciprocal of the total resistance is the 1. reciprocal of the total resistance is the sum of the reciprocals of the separate sum of the reciprocals of the separate resistors resistors 1/R T = 1/R 1 + 1/R 2 +1/R total current is the sum of the current through each resistor through each resistor I T = I 1 + I 2 + I potential difference is the same across each resistor each resistor V T = V 1 = V 2 = V 3 =... In other words, in a parallel circuit, resistance adds as reciprocals, voltage stays the same, and current splits. In other words, in a parallel circuit, resistance adds as reciprocals, voltage stays the same, and current splits. E = 12 V RT =RT =RT =RT = VT =VT =VT =VT = IT =IT =IT =IT = R1R1R1R1 R2R2R2R2 R3R3R3R3 R, V,VI, PT =PT =PT =PT = R3R3R3R3 R1R1R1R1 R2R2R2R2 P,W E = 12 V R T = 3.42 V T = 12 V I T = 3.50 A R1R1R1R1 R2R2R2R2 R3R3R3R3 R, V,VI, P T = 42 W R3R3R3R3 R1R1R1R1 R2R2R2R2 P,W The site linked herehere allows you here to build and test your own series, parallel, and/or combination circuits. For a complete interactive tutorial on electricity and magnetism, go here. here