Coulomb’s Law Electrostatic vs. Gravitational Coulomb’s Law Examples The Electric Field Electric Field Examples

Coulomb’s Law Fundamental property charge Positive and negative charge Units Coulombs (C) Force Law

Coulomb’s Law animation Fundamental Electrostatic Force You’d never get this much force from gravity!

Compare with gravitation Fundamental property mass Positive mass only Units kilograms (kg) Force Law

Electrostatic vs. Gravitational ElectrostaticGravitational Basic Law Similarities a) force along line joining a) product of charge (C) b) inverse square law a) force along line joining a) product of masses (kg) b) inverse square law Differences a) positive and negative charge b) attractive and repulsive c) strong (k=9 x 10 9 N-m 2 /C 2 ) a) positive mass only b) attractive only c) weak (G =6.67 x N-m 2 /kg 2 ) QuantizationCharge quantized 1.6 x CMass can be anything Vector SuperpositionExample 16-4 (page 448)example 5-12 (page 120)

Coulomb’s - Example 16.1

Coulomb’s Example – 1D Vector Addition

Coulomb’s Example – 2D Vector Addition (1)

Coulomb’s Example – 2D Vector Addition (2) Example 16-4 – XY Table (did last semester) ForceX-componentY-component F 32 0 N+ 330 N F N cos30 = 120 N-140N sin30 = -70 N Total120 N260 N

Coulomb’s Example – Problem 13 Charge Triangle

“Field” concept - Gravity

“Field” concept - Electrical Cellphone signal – Multiple users sharing same tower. – Why calculate each phone separately? 2 step process – 1. Calculate common “field”. – 2. Calculate each phone’s interaction with that “field”. “Field” equals # of “bars” you have!

Electrostatic vs. Gravitational Field

Electric FieldGravitational Field Field Concept Can be anythingUsually equal 9.8 m/s 2 Force & field F=q 2 E Force in field/opposite direction F= m 2 g Force in field direction Field DefinitionRatio of Force/charge Ratio of Force/mass, (simplifies to acceleration) Strength Electrostatic so strong appears on circuit-board scale Gravity so weak only appears on planetary scale Comment “E” quite interesting Varies all over the place “g” usually boring usually constant 9.8 m/s 2 Superposition Can superimpose continuously Wires, electrodes, circuit boards Can superimpose discretely Planets, etc

Electric Field - Example 16-8 (1)

Electric Field - Example 16-8 (2)

Electric Field Animation 2-D animation sites.googlegroups.com/site/physicsflash/Efield.swf?attachauth=ANoY7crCoduqPW1yrSvMtvv2qNVfA62NqyoNF1X8FY1ldipscty_- KXPmxmMyKYNdrruNd8vROoqOCxqee-i4LdS8Ct27vHfViZ597w8ETuqbnejUPkP7AiKqr4M-S3qn2VLzO2dQNl_KXv- Re0jQ5puGFnzKrPwZvuy0UkMwMU4QhXhJIIX4jWlWsQhQdgzqz-f17N3xQOXvEvfeWC1O- 3ObHX89WV72w%3D%3D&attredirects=1

Electric Field - Example 16-9 (1) Get magnitudes

Electric Field - Example 16-9 (2) XY table FieldX-componentY-component E2E2 0 N/C+5 x 10 6 N/C E1E x 10 6 N/C x 10 6 N/C Total+1.1 x 10 6 N/C x 10 6 N/C

Electric Field – Problem 16 Charge square