Electric Fields

Electric Fields

1. Electric Field Lines

   • Positive
   • Negative
   • Positive -> Negative

2. Coulomb's Law

   • The force between 2 charges (Q1 and Q2) at a distance, r is:
   • This can be simplified by lumping the constants together into a single constant (k)

3. Electric Field Strength (E)

   • An electric field is a region where forces act on charges. It is measured in Newtons per Coulomb
   • Substituting the force from Coulomb's law you get the equation for Electric Field strength of a certain charge:

4. Electric Fields with more than one charge

   • All you need to do is take one away from the other to get a resultant field
     • 2 charges Q1 and Q2 exert forces on a test charge
     • In terms of D and x

5. Electric Field between parallel Plates

   • Voltage is defined as the work done per unit charge
     • Work done is calculated by doing the force multiplied by the distance moved in the force direction
       • Since E = F/Q:
         • And since V = W/Q that means electric field strength is also measured in Volts per metre

6. Electric Potential, V

   • The electric potential, V, at a point is the work done per unit positive charge on a positive test charge when moved from a point infinitely far away from any charges to that position.
     • It can also be thought of as the amount of energy it would take to remove a negative charge from a positive field from that point
   • The work done to move such a charge is the electric force (from Coulomb's law) x distance it moves, r.
     • This then becomes:
   • Electric potential difference, ΔV
     • The electric potential difference (ΔV) between two points is numerically equal to the work done (ΔW) in moving a unit positive charge from the point at the lower potential to the point at the higher potential.
       • The work done, ΔW, to move a charge, Q, from one potential to another, ΔV, is:

7. Equipotentials and Potential Gradients

   • Equipotentials are at perpendicular to the electric field lines. In a uniform field the equipotentials are parallel (e.g. in between 2 plates). The electric field strength, E, is equal to the negative of the potential gradient (ΔV/Δr):

8. Comparing Electric and Gravity Fields

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