PHYS 0175 1st Edition Lecture 6Outline of Last Lecture II. Electric DipoleIII. Field of Electric DipoleIV. Electric Dipole in an external electric fieldV. External Torque on electric dipoleVI. Dipole Potential EnergyVII. Electric Field in Continuous Charge Distributiona. Rod b. Ringc. DiskOutline of Current Lecture VIII. Electron Oscillating about a ring of chargeIX. Electric Field of infinite charged plateX. Electric field between two infinite charged parallel platesXI. Acceleration of protonXII. Deflecting chargesCurrent LectureII. Electron Oscillating about a ring of chargea. If positively charged ring, electron will move from center along the axis of symmetry and oscillate along the ringb. E=kQz/(z^2+R^2)^1.5c. Assume distance z<<R radiusd. Force on electron=-(kQe/R^3)*zi. Part in () is the “spring” constant for electric fieldii. Also in N/me. Analogous to spring force F=kxf. Use the fact that angular freq=sqrt(k/mass electron)g. Freq =w(angular freq)/2piIII. Electric Field of infinite charged platea. Take the limit for the field of the charged solid disk as the radius goes toinfinityb. E=sigma/2*permittivity constantc. Sigma=areal charge density(C/m^2)d. Independent of distancei. Does not matter where the location is, field is always the sameIV. Electric field between two infinite charged parallel platesa. One positive and one negative plate separated a distance of equal magnitude chargesb. Electric field lines point away from positivec. Point toward negativesd. On left of leftmost plate and to the right of rightmost plateelectric field vectors cancel outi. Equal and oppositee. Only at the centerelectric field lines vectors will addi. Double, same directionii. Magnitude is independent of distance from plate!iii. Does not matter if particle is closer to one or the other, electric field will be the same for either location between the two oppositely charged platesiv. Enet=E+ + E- =sigma/permittivity constant=4pi*k*sigmaV. Acceleration of protona. If no charged plates, will be neutral and move along straight lineb. Gravity has almost no effect, too weak, proton is too smallc. If charged plates move towards negative plate and away from positive charge plate(deflect)d. Analogous to a parabolai. However can deflect up or downii. Has an acceleration that is constant1. Because Force and electric field are constant2. Can use kinematics equationsVI. Deflecting
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