ELECTRIC FORCE AND WORK

Fields Electricity and gravity both act at distance Have regions (called “fields”) where they – alter space – change how objects within the field behave More mass = stronger gravitational field, and more change caused by gravity More charge = stronger electric field, and greater change caused by electricity Fields are vectors (with magnitude and direction)

ELECTRIC FORCE AND WORK Electricity, like gravity, can act over distance

Gravitational force Law of Gravitation: Gravity is directly proportional to mass, and inversely proportional to distance between objects. It always acts toward center of mass (attractive) The more massive the object(s), the greater the gravitational force The more distance separating objects, the smaller the force

Newton’s Law of Universal Gravitation F = G. M 1 m 2 d 2 F = force m 1 = mass of one object m 2 = mass of second object d = distance G = × N.m 2 /kg 2 (G is a constant of gravity)

Electric force Acts between objects with charge, just as gravity acts between objects with mass Force can be either attractive or repulsive Lines of force drawn away from + charges and toward – charges As though protons push away, and electrons attract

Electric charges Electrically charges form fields Charges either – or +. Identical charges repel; opposite charges attract Amount of electric charge is measured in coulombs 1 C = 6.25 * electrons

Moving charges Moving a charge in uniform field creates temporary imbalance in placement of + and – charges, and causes imbalance Greater imbalance (called potential difference, or voltage) = greater force: – needed to hold charges in place, or – they exert when return to their balanced state s/DielectricBoundary/DielectricBadLinesFixed.png

Strength of electric field Place the letters of the particles in order from the one feeling the strongest effects of electric force to the one feeling the weakest effects.

Volts and voltage In electric systems, potential difference is “electric potential” measured in volts Voltage is like force in mechanical systems or pressure in fluid systems Voltage causes charge to move in electric systems. It is the prime mover in electric systems.

Current Flow of charge is current Flows until + and – charges equalized (no potential diff.) Current measured in amperes 1 A = 1 C/sec

Electric system components Voltage source (battery, generator) Control element (switch, rheostat) Load (light bulb, TV, whatever uses electricity) Conducting path (wires) Path must be closed for current to flow TS-Module htm

AC and DC Direct current – moves in 1 direction. Battery is voltage source fr. Negative cathode -> positive anode. Small appliances Alternating current – oscillates (back and forth) in wire. Generator is source. Cycle occurs 60 times/sec (60 Hz) in US. This is frequency. Large appliances use AC Current-Alternating-Current.png

Circuits Series (1 path for electrons to take) Parallel (more than 1 path for electrons to take)

Electric work Cannot see electric work, only results of it wgZ6IeuVmX4/Tb3VYpk0_fI/AAAAAAAAAZ8/US1X5RnRxTM/s1600/electroni c+devices.jpg

Electric work Measured in Joules 1 Joule = 1 volt * 1 Coulomb (J=1vq), how much voltage makes given amount of charge move Efficiency of electric devices always = work out work in and is always less than 100% Energy not put to useful work is lost as thermal energy

Electric rate Rate at which voltage makes charge move is current. Measured in amperes (A or I) 1 A = 1 coulomb / 1 sec sics/electricity/basic_electricity/basic_elec tricity.html#current

Coulomb’s Law F = K. q 1 q 2 d 2 F = force q = charge d = distance K = constant of charge Electric forces either attract or repel inverse-square-law1.png y/images/Coulomb_Law.gif

Coulomb’s Law What happens to electric force as charge increases? As distance increases?

Coulomb’s Law Electric force is directly proportional to charge, and inversely proportional to distance between objects (inverse square law) fieldlines.PNG

Electric field lines Describe the lines of force in each diagram