Electric Fields and Electric Energy

Electric Fields and Electric Energy

1. The Electric Field

   • MEANING: An electrically charged object sets up a force field around it; this force field is known as an electric field.
   • The electric field can be visualized
     • The direction of an electric field is away from a positive charge and toward a negative charge.
   • The electric field is the amount of force per change
     • magnitude of electric field = force on positive charge/amount of charge. Meaning, E = F/q0
       • Determining the Force on a Charge
         • force = amount of charge x electric field. Meaning, F = |q|E
   • Point charge electric fields decrease with distance
     • magnitude of electric field = k |charge| / (distance)^2 . Meaning, E = k |q| / r^2
   • 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 field such as the freshwater fish in Africa.
   • Simple rules are used for drawing electric field lines
     • 1. Electric field lines point in the direction of the electric field 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.
   • 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 charge connected in parallel to 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.
   • An object can be charged without ever touching it
     • The charging of an object without direct contact is referred to as charging by induction.

2. Electric Potential Energy and Electric Potential

   • MEANING: Mechanical work that is stored as electrical energy is referred to as electrical potential energy.
   • 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
     • charge in electric potential = charge in electric potential energy/charge. Meaning, ΔV = ΔPE/q
       • Understanding Voltage
       • Units of Voltage
         • The unit of electric potential, or voltage, is the volt (V).
   • Electric potential is related to the electric field
     • electric field = - change in electric potential/distance. Meaning, E = - ΔV/d
       • The electric potential decreases in the direction of the electric field. In addition, the electric potential doesn't change at all in t 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.

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