Week 2 Day 1 Concept Question Dipole Field Correct answer As you move to large distances r away from a dipole the electric eld will fall off as more rapidly than 1 r 2 Electric Dipole Moment Two Charges p q r q r qaj q aj 2qaj Dipole moment vector point from negative to positive charge Review Electric Field Lines Direction of eld at any point is tangent to eld line at that point Field lines point away from positive charges and terminate on negative charges Field lines never cross each other Total eld dipole background lines illustrate torque Field lines transmit tension Connection between dipole eld and constant eld pulls dipole into alignment Concept Question Dipole in Non Uniform Field Correct answer A dipole sits on a non uniform electric eld E Due to the electric eld this dipole will feel ANSWER Dipole in Uniform Field E E p 2qa cos sin j Total Net Force F F F qE q E 0 Torque on dipole r x F p x E rF sin 2a qE sin pEsin p tends to align with the electric eld Torque on Dipole Continuous Charge Distributions Break distributions into parts Q q dq E eld at P due to q E Superposition E E dE Continuous Sources Charge Density Volume V R L Area A wL Length L Group Problem Charge Densities A solid cylinder of length L and radius R is uniformly charges with total charge Q What is the volume charge density What is the linear charge density What is the relationship between these two densities and Example Finite Line of Charge Q L Q L E eld on perpendicular bisector Group Problem Finite Line of Charge Point P lies on perpendicular bisector of uniformly charged line of length L a distance s away The charge on the line is Q Find an integral expression for the direction and magnitude of the electric eld at P Concept Question Electric Field of Uniformly Charged Ring Correct answer A uniformly charged ring of radius a has total charge Q Which of the following expressions best describes the electric eld at the point P located at the center of the ring Worked Example Electric Field of a Uniformly Charged Ring A ring of radius a is uniformly charged with total charge Q Find the direction and magnitude of the electric eld at the point P lying a distance x from the center of the ring along the axis of symmetry of the ring De ne variables Write equation Integrate Final answer Concept Question Scaling and Electric Fields Correct answer You are told that the electric eld for a source of charges falls like 1 r far away from the source Which of the following sources could produce such an electric eld STOPPED HERE IN CLASS
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