Download ELECTRIC FIELDS AND POTENTIALS

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