Coulomb's Law

• What does Coulomb's Law describe?

  The electric force between two charges
• What does the electric field generated by charged particles do?

  It exerts a force on nearby charged particles
• How is the electrostatic force between two point charges defined?

  It is proportional to the product of the charges

  
• What is the relationship between electrostatic force and distance according to Coulomb's Law?

  It is inversely proportional to the square of their separation
• What is the formula for calculating the electrostatic force?

  F = $\frac{Q_1Q_2}{4\pi\epsilon_0r^2}$
• What does the variable F represent in Coulomb's Law?

  Electrostatic force between two charges
• What do Q1 and Q2 represent in the formula for Coulomb's Law?

  Magnitudes of the charges
• What does the variable r represent in Coulomb's Law?

  Distance between the centres of the charges
• What is ε0 in Coulomb's Law?

  Permittivity of free space
• How does Coulomb's Law relate to Newton's law of gravitation?

  Both follow an inverse square law
• What happens to the electrostatic force between two like charges?

  They experience repulsion
• What happens to the electrostatic force between two opposite charges?

  They experience attraction

  
• What is the value of the permittivity of free space ε0?

  8.85 × 10$^{-12} \text{ F/m}$
• What is the Coulomb constant k in Coulomb's Law?

  k = $\frac{1}{4\pi\epsilon_0}$
• What is the value of k in a vacuum?

  8.99 × 10$^9 \text{ N m}^2/\text{C}^2$
• What are the characteristics of electric forces compared to gravitational forces?

  • Electric forces can be attractive or repulsive
  • Gravitational forces are only attractive
  • Both follow an inverse square law
• How do you calculate the charge of an alpha particle?

  Q = 2e = 2 × (1.60 × 10$^{-19}$)
• How do you calculate the charge of a gold nucleus?

  Q = 79e = 79 × (1.60 × 10$^{-19}$)
• What is the first step in calculating the electric force between two charges?

  Write down the known quantities
• What are the conditions for applying Coulomb's Law?

  • Charges must be point charges
  • Separation must be much larger than their sizes
  • Distance r is measured from the centres of the charges
• What are the characteristics of electric field lines around a spherical conductor?

  • Identical to those around a point charge
  • Radial lines directed away for positive charge
  • Radial lines directed towards for negative charge

  
• Why can't Coulomb's Law be used for irregularly shaped objects?

  Charges are not uniformly distributed
• What similarities and differences exist between electric fields and gravitational fields?

  Similarities:

  • Both can exert forces
  • Both follow an inverse square law

  
  

  Differences:

  • Electric forces can be repulsive
  • Gravitational forces are always attractive