Electric Field 1

• Applications of capacitors


  • Radio circuits for tuning
  • Ignition system of motor vehicles
  • Elimination of sparks when a circuit containing inductance is suddenly opened e.g. in induction coils
• Electric field


  An area around a charge, q₁, in which another charge q₂ can experience a force
• Force, F, between two charges q₁ and q₂

  F = (1/4πε₀)(q₁q₂/r²), where r is the distance between the two charges and 1/4πε₀ is a constant = 9.0 × 10⁹ Nm²/C²
• Electric line of force


  An imaginary line whose direction at any point in the electric field is the same as the direction a small positive charge would follow if placed at that point in the electric field
• Electric field intensity, E

  The force per unit positive charge. It is a vector.
• Electric Potential, V


  The work done in bringing unit positive charge from infinity to the point
• Potential difference (P.d) between two points A and B

  The work done in bringing unit positive charge from B to A where A is at a higher potential than B
• Capacitor


  A device for storing electric charge. The capacitance of a capacitor is the charge per unit P.d. between the plates of a capacitor (C=Q/V). The capacitance of a parallel plate capacitor is dependent on (i) the area of the plates (ii) the distance of separation between the plates and (iii) the dielectric between the plates.
• Connecting capacitors in parallel


  C = C₁ + C₂ + C₃ + ...
• Energy stored in a capacitor

  W = (1/2)CV²
• The net capacitance in the circuit above is 3 F
• The electric potential energy between two protons of charge q and at a distance r apart is (1/4πε₀)(q²/r)
• A work of 30 Joules is done in moving 20 milliCoulombs of charge from point A to point B in an electric field
• A charge of 1.0 x 10-5 C experiences a force of 40 N at a certain point in an electric field
• Electric Force between Point Charges

  F = k \* (q1 \* q2) / r^2
• Electric Field Intensity (E)


  E = F / q
• Electric Field Intensity (E) formula

  E = k \* (q1 / r^2)