PHYS 0175 Lecture 3 Outline of Last Lecture II. Electric Charge and the structure of matterIII. Conductors and InsulatorsIV. Principles of chargeV. Methods of Charginga. Contactb. Induction VI. Forces between chargesa. Coulomb’s LawVII. Electric Force vs Gravitational ForceOutline of Current Lecture VIII. Two Point charges in two dimensionsIX. Principle of Linear Superposition of electrostatic forcesX. Torque problems with electrostatic forcesXI. Electric Fielda. Gravity analogyCurrent LectureXII. Two Point charges in two dimensionsa. X and Y directionsb. Must take components of both and use trigc. Use Pythagorean theorem for resultant vectord. Use inverse tangent to find the direction(angle)e. In a coordinate system, must also find the directional r-hat vector along with the electrostatic force’s magnitudei. Suppose one objects lies on the x-axis and the other on the y-axisii. For a force of F21(force of 2 acting on 1) r-hat=(r1-r2)/r where r is the distance between the two charges, r1 and r2 are distances from the originXIII. Principle of Linear Superposition of electrostatic forcesa. To find the net force acting on a particle, one must sum up the forces vectoricallyi. Take x and y components of each particles’ force acting onparticle of interest, sum them up and then find the resultant using Pythagorean theoremXIV.Torque problems with electrostatic forcesa. Must consider the electrostatic forces that act about a pivot pointb. Clockwise is negative, counter clockwise positivec. T=rxF(torque)XV. Electric Fielda. In order to generate an electrical field, there needs to be a test particle A and a point particle B which creates the electrical field around the area it is inb. Electric field(E)=F/qi. Force per unit charge(N/C)ii. The greater the charge, the greater the force1. F=qE2. This equation is analogous to F=mg for the gravitational field3. As more particles are within range of the particle producing the electric field, the electric field itself becomes strongerc. Charge q that generates electrical field is usually much smaller compared to the test
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