Electric Fields and Electric Energy

Electric Fields and Electric Energy

1. Electric Potential Energy and Electric Potential

   • Electric Fields store mechanical work
     • Opposite Charges
       • Separating two charges that attract each other requires mechanical work.
     • Like charges
       • Moving two charges that repel each other closer together requires mechanical work.
     • Calculating work done in an electric field
   • Voltage is the electric potential energy per change
     • Unit of voltage
       • The unit of voltage is the volt "V"
     • Understanding voltage
   • Electric potential is related to the electric field
     • Electric field= - change in electric potential/ distance.
       • The electric potential decreases in the direction of the electric field. In addition, the electric potential doesn't change in the direction perpendicular to the electric field.
   • Energy is conserved in electrical systems
     • General equation for energy conservation
       • Ki + Ui = Kf = Uf
     • Applying energy conservation
     • Direction of acceleration in an electric field.
       • Positive charges accelerate in the direction of decreasing electric potential.
       • Negative charges accelerate in the direction of increasing electric potential.
   • Electric potential decreases with distance
     • Electric potential = k (charge/distance). Meaning, V= k (q/r)
   • Electric potentials combine by simple additions
     • The total electric potential due to two or more charges is equal to the algebraic sum of the potentials due to the individual charges.
   • Mechanical work that is stored as electrical energy is referred to as electric potential energy.

2. Electric Field

   • The electric field can be visualized
     • The direction of an electric field is away from a positive charge and towards a negative charge.
   • Electric fields add together
     • When a system consists of several charges, the total electric field is found by superposition.
       • Applying Superposition
   • Some animals can produce and detect electric fields.
     • Many aquatic creatures are capable of producing electric fields.
   • Simple rules are used for drawing an electric field lines
     • 1. Electric field lines point in the direction of the electric vector "E" at every point.
       • 2. Electric field lines start at positive (+) charges or at infinity
         • 3. Electric field lines end at negative charges (-) or at infinity
           • 4. Electric field lines are closer together where "E" has a greater magnitude.
             • 5. The number of electric field lines entering or leaving a charge is proportional to the magnitude of the charge.
   • An object can be charged without ever touching it.
     • Charging by induction.
   • Electric fields have distinctive shapes and patterns
     • Electric dipoles
       • Is defined as a couple of opposite charges +q and -q separated by a distance d
     • Infinite plates and parallel- plate capacitors
       • A parallel plate capacitor is an arrangement of two plates with opposite charges connected in parallel with one another separated by a finite distance.
   • Excess charge moves to a conductor's outer surface
     • The distribution of charge on the surface of a conductor guarantees that the electric field within the conductor is zero.
   • Point charge electric fields decrease with distance.
   • The electric field is the amount of force per change.
     • Determining the force on a charge
       • Force= amount of charge x electric field. Meaning, F= |q|E

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