Chapter 21 - The Electric Field I Discrete Charge Distributions | Concordia University Wisconsin

University:
Concordia University Wisconsin
Course:
PHYS 1524 | General Physics II
Academic year:

2021
Views:

233

Pages:

2
Author:

Kevin Riddle

Electricity Chapter 21 - The Electric Field I: Discrete Charge Distributions ● Coulomb ( ) - SI unit of charge [elemental charge, , is the smallest unit of charge (i.e. - proton or electron) and it indicates that CHARGE IS QUANTIZED]. More commonly used units are the microcoulomb ( ● ● ) or nanocoulomb ( ) Law of Charges: opposite charges attract & like charges repel = electric force (electromagnetic analog of gravity - force exerted from one charged particle on another) ● = electrostatic constant ( o ). Alternate form: = The permittivity of vacuum. How easily the electric force can go through a certain substance. ● Coulomb's Law - in a vacuum. (i.e.- the electric force is the electrostatic constant ( ) times the product of charge 1 ( ) and charge 2 ( ) divided by the distance ( ) between the two charges). Same form as the Gravity formula. ( o ). Expanded form: . Applies to POINT CHARGES. Uniformly charged spherical objects behave like point charges from their surface. ● Field Strength ( . Measured in ) - electromagnetic analog of . Thus, in . For point masses. Thus: ● Electric field diagrams - Lines representing the direction of the electric force acting on a positively charged particle are placed at that location. Near the source, the field lines are closer, meaning that the force is stronger. Since , then (where is the charge of the source of the field, not of the positively charged particle at that location). This is the electric field around a point charge with charge . Generally, field lines point from positive to negative. Field lines can never cross; they only interact to create new, averaged, field lines. o Dipoles - A dipole is the force tangent to the curved lines. Remember, it's the direction of the force, not necessarily where it will spread out. Uneven charges will cause the arrows to lean towards the larger charge. o Two like charges - an uncharged spot exists in the center: any test charge will remain stationary if placed in the direct center as the forces exert o . Uniform Field Strength - This occurs between two parallel and oppositely charged plates. Field lines are parallel so thus the field strength stays constant. For a sample problem, click here. ● Electric Dipole Moment -charges an & separated by distance . In field, dipole experiences torque: o Dipole Moment torque: where points from to . Thus