Electric Fields

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• Electric field: region of space around an object that has the property of charge in which another object that also has charge experiences a repulsive or attractive force, that extends to infinity, and weakens over time, as per the inverse square law
• 2 types of charge
  • Positive
  • Negative
• 3 states of charge
  • Positive
  • Negative
  • Neutral
• Some particles have only 1 state of charge
  • Protons are always positive
  • Neutrons/neutrinos are always neutral
  • Quarks are always charged
  • Electrons are always negative
• Neutral objects are made of negative and positive components

Electric field diagrams

• Charge is assumed to be uniform
• Uniform distribution
• MUST KNOW

Field line rules

1. They’re arrows, not lines
2. For point charges, field density is uniform, thus lines must be evenly distributed around surface
3. Field lines start/end at the surface
4. Field lines should start/finish perpendicular to surface
5. Number of field lines indicates field density
6. Minimum of 4 lines recommended (not required)
7. Direction of field lines are determined by hypothetical test charge
8. Field lines cannot touch or cross

$F_{ϵ}=\frac{k{q}_1{q}_2}{r^2}=\frac{1}{4\pi {ϵ}_0}\frac{q_1{q}_2}{r^2}$

• Electronic constant for a vacuum or air = ${ϵ}_0=8.85\ast 10^{-12}{\text{ F m}}^{-1}$

$E=\frac{F}{q}{\text{ N C}}^{-1}$

$E=\frac{\Delta V}{d}{\text{ V m}}^{-1}$

$\Delta E=Fd=Vq$