Electric Fields

A static charge on an object will create an electric field. Learn to draw electric fields around single and multiple charges and solve for their value.

Electric Field Basics

  • Electrical Field (E): an area of electrical influence around a charged object.
  • Variable (E)
  • Unit: newton per coulomb (N/C)
Electric Field Variables
Name Variable MKS Unit Unit Abbreviation
Electrical Field E Newton divided by Coulomb N/C
Force N Newton N
Charge q Coulomb C
Distance d Meter m

Drawing Electric Fields

Electric fields are drawn to represent the way a positively charged particle would move if placed in a field represented by the a or multiple standing charges.

  • Lines are drawn to represent the field
  • Spacing between the lines show field strength
  • Arrows are drawn to represent directions of the field
  • Arrows point away from the positive and toward the negative in the direction a positive charge would travel in the field
Electric Field Drawings

Electric Field Animations

In these animations the fields are presented at the beginning of the animation.  Later a tiny positive charge moves in the field to show what the lines and arrows represent.

Electric field created by a positive standing charge
Electric field created by a negative standing charge
Electric field created by a positive and negative standing charge close to each other
Electric field created by two positive standing charges next to each other
Electric field created by two standing negative charges next to each other

Equations Variables and Units

Electric Field Equations

Variable: Name (unit)

E: electrical field  (N/C)

F: force (N)

Q: charge (C)

k: constant (For air, k = 9.0 x 109 N·m2/C2)

d: distance (m)

Example Problems

1. You pull a wool sweater over your head, which charges as it created friction with your cotton shirt.  What is the electrical field at a location where a 1.30 x 10-19 C- piece of lint experiences a force of 3.2 x 10-9 N as it floats?

Electrical Field Problem 1

(Click the picture to see a larger view of the work)

2. How far are you from a charge of 3.25 x 10-6 Coulombs when there is an electrical field of 18.1 N/C?

6

(Click the picture to see a larger view of the work)

 

Shielding

When you have a conductive path around an object.  Shielding occurs because electrons (- charge) stay as far away from each other and stay on the outside.  Electrical fields balance out and on the inside there will be no electrical field.

  • All charge lies on the surface of a conductor
  • Electrical field inside a conductor is zero

This effect protects you from getting electrocuted if you are inside a metal car that gets hit by lightning.  People can wear conductive clothing surrounding their entire body and play with the phenomenon that is created with electrostatics and the current that would occur as charge is discharged.

Car Getting Struck By Lightning

When a car gets struck by lightning the current travels around the cars conductive outside and arcs to the ground.  Since the current is traveling around, the person in the car is safe and not experiencing the arc.  Remember that an arc is the lightning with the sound and light that you see and hear during a violent grounding through the air.

Lightning Battle With Tesla Coils

Current passes around the people wearing these suits keeping the individuals inside them safe.  Anyone outside the conductive suit on a Tesla coil would be in danger without and not shielded.

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