Electric Fields

Electric Fields

Definition

• Electric field E at a point: force per unit positive charge
  • E = F / q
  • Units: N/C (newtons per coulomb)
• Vector quantity: direction = direction of force on positive test charge

Coulomb's Law

• Force between two point charges:
  • F = k |q₁ q₂| / r²
  • k ≈ 8.99 × 10⁹ N·m²/C² (Coulomb's constant)
  • Force is attractive for opposite charges, repulsive for like charges

Field Line Direction

• Field lines originate on positive charges and terminate on negative charges
• Direction: tangent to field line at any point gives direction of E
• Density of lines: proportional to field strength (closer lines → stronger field)
• Lines never cross