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 13.1 Electric Charge 13.2 Electric Force 13.3 Electric Field 13.4 Electric Potential

 13.5 Conductors and Insulators 13.6 Key Formulas 13.7 Practice Questions 13.8 Explanations
Electric Field
An electric charge, q, can exert its force on other charged objects even though they are some distance away. Every charge has an electric field associated with it, which exerts an electric force over all charges within that field. We can represent an electric field graphically by drawing vectors representing the force that would act upon a positive point charge placed at that location. That means a positive charge placed anywhere in an electric field will move in the direction of the electric field lines, while a negative charge will move in the opposite direction of the electric field lines. The density of the resulting electric field lines represents the strength of the electric field at any particular point.
Calculating Electric Field
The electric field is a vector field: at each point in space, there is a vector corresponding to the electric field. The force F experienced by a particle q in electric field E is:
Combining this equation with Coulomb’s Law, we can also calculate the magnitude of the electric field created by a charge q at any point in space. Simply substitute Coulomb’s Law in for , and you get:
Drawing Electric Field Lines
SAT II Physics may ask a question about electric fields that involves the graphical representation of electric field lines. We saw above how the field lines of a single point charge are represented. Let’s now take a look at a couple of more complicated cases.
Electric Fields for Multiple Charges
Just like the force due to electric charges, the electric field created by multiple charges is the sum of the electric fields of each charge. For example, we can sketch the electric field due to two charges, one positive and one negative:
Line Charges and Plane Charges
Suppose we had a line of charge, rather than just a point charge. The electric field strength then decreases linearly with distance, rather than as the square of the distance. For a plane of charge, the field is constant with distance.
 Jump to a New ChapterIntroduction to the SAT IIIntroduction to SAT II PhysicsStrategies for Taking SAT II PhysicsVectorsKinematicsDynamicsWork, Energy, and PowerSpecial Problems in MechanicsLinear MomentumRotational MotionCircular Motion and GravitationThermal PhysicsElectric Forces, Fields, and PotentialDC CircuitsMagnetismElectromagnetic InductionWavesOpticsModern PhysicsPhysics GlossaryPractice Tests Are Your Best Friends
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