Go Back   Physics Help Forum > High School and Pre-University Physics Help > Electricity and Magnetism

Electricity and Magnetism Electricity and Magnetism Physics Help Forum

Like Tree6Likes
  • 2 Post By HallsofIvy
  • 2 Post By studiot
  • 1 Post By Pmb
  • 1 Post By Pmb
Reply
 
LinkBack Thread Tools Display Modes
Old Feb 27th 2018, 11:50 AM   #1
Junior Member
 
TyrannosaurusWreck's Avatar
 
Join Date: Nov 2017
Location: The Jurassic Forests
Posts: 25
Electric Fields

Can anyone explain how to find electric fields caused by multiple charges at a specified position? I keep getting wrong answers when I try to do those problems, if someone could just break down how to go about them it'd be a big help! Thanks!
TyrannosaurusWreck is offline   Reply With Quote
Old Feb 27th 2018, 01:56 PM   #2
Senior Member
 
Join Date: Aug 2010
Posts: 336
The "electric field" is a vector field that, at each point, if multiplied by a charge, gives the force vector on that charge at that point.

If you have q1 at point A, charge q2 at point B, charge q3 at point C, etc., then the electric field at point P is the sum of forces on a unit charge by charges q1, q2, and q3.

Letting V1 be the vector from point P to A, The force on the unit charge at P due to charge q1 is q1V1/|V1|, where |V1| is the length of vector V1. Similarly if V2 is the vector from point P to B, the charge on the unit charge at P due to charge q2 is q2V2/|V2| and if V3 is the vector from point P to C, the charge on the unit charge at P due to charge q3 is q3V3/|V3|.

The electric field due to all three charges, at point P, is the vector sum q1V1/|V1|+ q2V2/|V2|+ q3V3/|V3|.
HallsofIvy is offline   Reply With Quote
Old Feb 27th 2018, 02:36 PM   #3
Senior Member
 
Join Date: Apr 2015
Location: Somerset, England
Posts: 980
Two notes to add the Halls excellent summary.

The process is called superposition, which is a posh word to say that you can find the field due to each charge individually (or acting on their own) and add them up. But this must be vector addition since E (the electric field vector) is a vector.

Hall mentioned three charges Q1, Q1 and Q3 but hidden is a fourth one the unit test charge. This is not considered to contribute to the sum.
studiot is offline   Reply With Quote
Old Feb 27th 2018, 04:21 PM   #4
Pmb
Physics Team
 
Join Date: Apr 2009
Location: Boston's North Shore
Posts: 1,548
Originally Posted by TyrannosaurusWreck View Post
Can anyone explain how to find electric fields caused by multiple charges at a specified position? I keep getting wrong answers when I try to do those problems, if someone could just break down how to go about them it'd be a big help! Thanks!
For just this purpose I created a website to explain things for people such as yourself. I recommend reading this page:

Laws of Electrodynamics

It has everything you might want to know. If not then let me know and when I'm able to I'll add it in.
TyrannosaurusWreck likes this.
Pmb is offline   Reply With Quote
Old Feb 27th 2018, 05:31 PM   #5
Junior Member
 
TyrannosaurusWreck's Avatar
 
Join Date: Nov 2017
Location: The Jurassic Forests
Posts: 25
Thank you all!
Your explanations made a lot more sense than my textbooks, but for some reason I'm still not getting one problem... I'll post it tomorrow with my attempt at it.
TyrannosaurusWreck is offline   Reply With Quote
Old Feb 27th 2018, 05:33 PM   #6
Junior Member
 
TyrannosaurusWreck's Avatar
 
Join Date: Nov 2017
Location: The Jurassic Forests
Posts: 25
Originally Posted by Pmb View Post
For just this purpose I created a website to explain things for people such as yourself. I recommend reading this page:

Laws of Electrodynamics

It has everything you might want to know. If not then let me know and when I'm able to I'll add it in.
I couldn't find electric fields, what are they under on your site? Sorry!
TyrannosaurusWreck is offline   Reply With Quote
Old Feb 27th 2018, 06:03 PM   #7
Pmb
Physics Team
 
Join Date: Apr 2009
Location: Boston's North Shore
Posts: 1,548
Originally Posted by TyrannosaurusWreck View Post
I couldn't find electric fields, what are they under on your site? Sorry!
When you have a problem like that use the web page search function.

But you can just scroll down to the section on Coulomb's law. Then see Eq. (7)
TyrannosaurusWreck likes this.
Pmb is offline   Reply With Quote
Reply

  Physics Help Forum > High School and Pre-University Physics Help > Electricity and Magnetism

Tags
electric, fields



Thread Tools
Display Modes


Similar Physics Forum Discussions
Thread Thread Starter Forum Replies Last Post
Capacitors and electric fields ZergLurker Advanced Electricity and Magnetism 2 Feb 24th 2010 12:55 AM
Electric Fields Apprentice123 Advanced Electricity and Magnetism 8 May 17th 2009 01:20 PM
Electric fields LS09 Electricity and Magnetism 1 Feb 6th 2009 09:20 PM
electric fields physics123456 Advanced Electricity and Magnetism 1 Jan 18th 2009 06:37 PM
Sketching the electric fields soccerdude28 Advanced Electricity and Magnetism 0 Nov 1st 2008 11:58 AM


Facebook Twitter Google+ RSS Feed