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Transcript
ELECTRIC FIELDS AND POTENTIALS THE NEXT STEP ELECTRIC FIELDS • THE FORCE FIELD THAT SURROUNDS A CHARGE. • EXAMPLE - VAN DE GRAPH GENERATOR • ANOTHER TYPE OF FIELD IS GRAVITATIONAL FIELD. ELECTRIC FIELD • THE SPACE AROUND EVERY ELECTRIC CHARGE IS FILLED WITH A FORCE DUE TO THE ELECTRIC CHARGE AND WE CALL THIS THE ELECTRIC FIELD. • THIS FORCE CAN BE DESCRIBED BY THE INTERACTION BETWEEN ONE CHARGE AND THE ELECTRIC FIELD SET UP BY THE OTHER. ELECTRIC FIELD LINES • ELECTRIC FIELDS HAVE: • DIRECTION • MAGNITUDE MAGNITUDE • MAGNITUDE- MEASURED IN N/C OR V/m • MEASURED BY USING A SMALL TEST CHARGE IN AN ELECTRIC FIELD. THE FORCE IS THE STRONGEST WHERE THE FIELD IS THE STRONGEST AND THE WEAKEST WHERE THE FIELD IS THE WEAKEST. DIRECTION • THE DIRECTION OF THE ELECTRIC FIELD IS FROM POSTIVE TO NEGATIVE. • THE ELECTRIC FIELD JUST OUTSIDE A CHARGED CONDUCTOR IS PERPENDICULSR TO THE CONDUCTOR’S SURFACE. • AN IRREGULARLY SHAPED CONDUCTOR, ELECTRIC FIELD LINES ALSO CALLED LINES OF FORCE • REPRESENT THE STRENGTH OF THE MAGNETIC FIELD. • THE MORE LINES THE STRONGER THE FIELD. • NO TWO FIELD LINES CAN CROSS EACH OTHER. + - OPPOSITE CHARGES • FROM POSITIVE TO NEGATIVE + - LIKE CHARGES • LIKE CHARGES REPELL + PLATES • POSITIVE TO NEGATIVE + + + + + + + + + + + - - ELECTRIC SHIELDING • ON A HOLLOW OBJECT CHARGE IS DISTRIBUTED EVENLY ON THE OUTSIDE SURFACE. • THE ELECTRIC FIELD IS OUTSIDE THE SPHERE • THE ELECTRIC FIELD INSIDE THE SPHERE IS ZERO. NONSPERICAL OBJECTS • THE ELECTRIC FIELD WILL NOT BE DISTRIBUTED EVENLY. IT TENDS TO BUILD UP AT SHARP TURNS OR CORNER. • THE ELECTRIC FIELD INSIDE WILL STILL BE ZERO. • HOLLOW OBJECTS ARE USED TO SHIELD SENSITIVE ITEMS. CAN YOU SHIELD GRAVITY? • THERE IS NO WAY TO SHIELD GRAVITY BECAUSE GRAVITY ONLY ATTRACTS. • GRAVITY CAN BE CANCELED INSIDE A PLANET OR BETWEEN PLANETS. POTENTIAL ENERGY • • • • REMEMBER: WORK = CHANGE IN K.E. F X D = ½ MV2 CHANGE IN P.E. = CHANGE IN K.E. ELECTRIC POTENTIAL ENERGY • CHARGES CAN HAVE P.E. BY VIRTUE OF WHERE THEY ARE LOCATED WITHIN THE ELECTRIC FIELD. • WE CALL IT ELECTRIC POTENTIAL ENERGY. • IF A CHARGE IS HELD STILL IN AN ELECTRIC FIELD IT WILL HAVE ELECTRIC POTENTIAL ENERGY, WHEN IT IS ALLOWED TO MOVE, THE P.E. WILL CONVERT TO K.E. ELECTRIC POTENTIAL • THE TOTAL ELECTRICAL POTENTIAL ENERGY DIVIDED BY THE AMOUNT OF CHARGE. • AT ANY LOCATION THE P.E. PER CHARGE WILL BE THE SAME. • ELECTRIC POTENTIAL IS MEASURED IN VOLTS. • COMMONLY CALLED VOLTAGE FOR ALESSANDRO VOLTA – FAMOUS FOR CREATING BATTERIES. EQUATION • ELECTRIC POTENTIAL = ELECTRICAL POTENTIAL ENERGY/CHARGE • V = W/Q • 1 VOLT = 1JOULE/COULOMB ELECTRIC POTENTIAL ENERGY V.S. ELECTRIC POTENTIAL • ELECTRIC POTENTIAL ENERGY BUILDS ON THE OUTSIDE OF THE VAN DE GRAFF GENERATOR. • CAN YOU TAKE THE CHARGE OFF OF THE GENERATOR WITHOUT HURTING YOURSELF? • ELECTRIC POTENTIAL PROVIDES THE ELECTRON FLOW TO POWER THE GENERATOR. • CAN YOU TOUCH A BARE WIRE COMING FROM THE OUTLET TO THE GENERATOR WITHOUT BEING HURT? CAPACITANCE • ELECTRICAL ENERGY STORAGE • STORED IN A CAPACITOR • CAPACITOR – A SET OF PLATES SEPARATED BY A SPACE. • THE CHARGE IS STORED BETWEEN THE PLATES. • THE ENERGY STORED COMES FROM WORK REQUIRED TO CHARGE IT. • DISCHARGE OF A CAPACITOR CAN BE A SHOCKING EXPERIENCE. FOLLOW UP QUESTIONS • PHYSICS – PAGE 529; 1-20 • PRE AP PHYSICS – PAGE 642, 1-5; 652, 1-5; PAGE 654, 1-10 • ANSWER IN COMPLETE SENTENCES