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Summer session 1 c palmer july 2

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Unformatted text preview: ysics 1B - Summer Session 1 - C. Palmer July 2, 2013 26   In Region I, the field from q2 is in the –x direction (away from positive charge) and the field from q1 is in the +x direction (toward negative charge).   How do they balance?   |q2|>|q1| but close to q1 its field is very large, and so close to q1 the total field is positive. Region I Region II q1=- 1.0μC x=- 2cm x=0 Region III q2=+4.0μC x=+2cm +x Physics 1B - Summer Session 1 - C. Palmer July 2, 2013 27   Far from the charges the distance will be comparable but the |q2|>|q1| and so q2 dominates the field (-x dir) far.   Where is the electric field equal to 0 on the x-axis?   Somewhere in Region I. Region I Region II q1=- 1.0μC x=- 2cm x=0 Region III q2=+4.0μC x=+2cm +x Physics 1B - Summer Session 1 - C. Palmer July 2, 2013 28   Where is the electric field equal to 0 on the x- axis?   Somewhere x<-2.0cm   Follow r-hat ˆ r1 q1=- 1.0μC x=- 2cm x=0 q2=+4.0μC x=+2cm +x ˆ r2 Physics 1B - Summer Session 1 - C. Palmer July 2, 2013 29   Where is the electric field equal to 0 on the x- axis?   Somewhere x<-2.0cm   Follow r-hat ˆ r1 ˆ ˆ r1 = − x ˆ ˆ r2 = − x q1=- 1.0μC x=- 2cm x=0 q2=+4.0μC x=+2cm +x ˆ r2 Physics 1B - Summer Session 1 - C. Palmer July 2, 2013 30   Where is the electric field equal to 0 on the x- axis?   Somewhere x<-2.0cm q1=- 1.0μC E1x=- 2cm E2 x=0 q2=+4.0μC x=+2cm +x Physics 1B - Summer Session 1 - C. Palmer July 2, 2013 31   Where is the electric field equal to 0 on the x- axis?   Somewhere x<-2.0cm ETotal = E1 + E2 ke q1 ke q2 ˆ ˆ = r1 + r2 2 2 ( x − x1 ) ( x − x2 ) q1=- 1.0μC x=- 2cm x=0 q2=+4.0μC x=+2cm +x Physics 1B - Summer Session 1 - C. Palmer July 2, 2013 32   Where is the electric field equal to 0 on the x- axis?   Somewhere x<-2.0cm ETotal = E1 + E2 ke q1 ke q2 ˆ ˆ = (− x) + (− x) 2 2 ( x − x1 ) ( x − x2 ) q1=- 1.0μC x=- 2cm x=0 q2=+4.0μC x=+2cm +x Physics 1B - Summer Session 1 - C. Palmer July 2, 2013 33   Where is the electric field equal to 0 on the x- axis? Somewhere x<-2.0cm q1 q2 − − =0 2 2 ( x − x1 ) ( x − x2 ) q1 q2 =− 2 ( x − x1 ) ( x − x 2 )2 q ( x − x1 )2 = − 1 ( x − x2 )2 q2 q1=- 1.0μC x=- 2cm 1 ( x + 0.02 m ) = ( x − 0.02 m )2 4 1 x + 0.02 = ( x − 0.02 ) = 0.5 x − 0.01 2 x = −0.06 m = −6 cm 2 x=0 q2=+4.0μC x=+2cm +x Physics 1B - Summer Session 1 - C. Palmer July 2, 2013 34   Conductors – – – – – – – – – – – –   Excess negative (or voids resulting in positive) charge on a conductor repel each other.   They move to minimize/balance the force on all charge.   The outcome is that charge is distributed ON THE SURFACE of the conductor.   If the surface is pointy, then that is farther anyway and the charge accumulates there.   If there is significant symmetry, then on a smooth conductor the charge will be uniformly distributed. Physics 2B - Summer Session 2 - C. Palmer August 5, 2013 35   Inside of a conductor the electric field is zero.   The electric field outside a conductor is normal (perpendicular) to the surface. – – – |E|=0 – – –   This is in accordance to the rules for field lines   The lines begin/end at charges. Physics 1B - Summer Session 1 - C. Palmer July 2, 2013 36   Go to khanacademy.org   You can login with a google account, facebook or your email address   Go to Learn Science & Engineering Physics   Then go to “Electricity and magnetism” on the right   This site has some great lectures/walk-through of problems   “Electrostatics (part 1): Introduction to Charge and Coulomb's Law” ~ 15 minutes   Charge and Coulomb’s Law example   Also, start the chapter 21 problems   It’s a good idea to get ahead now. Physics 2B - Summer Session 2 - C. Palmer August 5, 2013 37...
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This note was uploaded on 09/10/2013 for the course PHYS 2B 2b taught by Professor Hirsch during the Summer '10 term at UCSD.

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