Electric Fields

• Electric Field: A region of space where a charge will experience an electrostatic force.
• Electric Field Strength: The force per unit charge on a positive test charge placed at that point.
• Units of Electric Field Strength

  NC^-1
• Direction of Electric Field Line: The direction of the force exerted on a positive test charge.
• Spacing of Electric Field Lines


  Field strength.
• Test Charges


  Positive.
• Equation E = V/d: To find the uniform field strength between two parallel plates.
• Uniform Electric Field: A region of space in which the electric field strength is the same at all points.
• Units Equivalent to V/m

  Vm^-1
• Electric Potential Difference: The work done per unit positive charge in moving between two points.
• Relationship between Electric Potential Energy and Electric Potential: EPE = V x q where q is the charge in the field.
• Absolute Electric Potential of a Point: The work done per unit charge on a positive test charge to move from infinity to that point in the field.
• Absolute Electric Potential at Infinite Distance from 1C Charge: 0 J C^-1
• Electrical Potential Gradient: The change in potential per unit distance.
• Relationship between Field Strength and Potential: Field strength is equal to the negative of the potential gradient.
• Coulomb's Law: The force between two point charges is proportional to the product of the two charges and inversely proportional to the square of their separation distance.
• Relationship between Electrostatic Force and Separation Distance: It is inversely proportional to the square of separation OR inverse square law.
• Radial Field: An electric field generated by a point charge OR a field that obeys the inverse square law.
• Electrical Potential


  Scalar.
• Electric Field Strength


  Vector.
• Neutral Point in an Electric Field: A point at which the resultant field strength is zero.
• Equation V = Q/(4Eo*r): To find the potential around a point charge/in a radial field.
• Effect on Potential when Distance from Point Charge is Doubled: It is halved.
• Equation E = Q/(4Eo*r): To find the field strength around a point charge/in a radial field.
• Effect on Field Strength when Distance from Point Charge is Doubled: It is quartered.
• Relationship between Potential and Distance from Point Charge: Potential is inversely proportional to distance.
• Similarity between Electric and Gravitational Fields: Both obey inverse square law for field strength and distance.
• Differences between Electric and Gravitational Fields: Gravitational fields act on masses, electric fields on charges; electric fields are much stronger.
• What symbol represents the permittivity of free space?

  𝜀₀
• How can air be treated when calculating the force between two particles?

  As a vacuum
• Where can the charge of a charged sphere be assumed to be located?

  At the centre
• Which force is stronger: gravitational or electrostatic?

  Electrostatic force
• Electric field lines always go from which charge to which charge?

  Positive charge to negative charge
• What is electric field strength?

  Force per unit charge at a point
• How is the magnitude of electric field strength (E) calculated in a uniform electric field?

  Potential difference (V) / distance (d)
• What is the trajectory of a particle entering a uniform field at right angles?

  It is parabolic
• How is electric potential related to electric field strength?

  E = ΔV/Δr
• What does the equation E = ΔV/Δr represent?

  • Electric field strength (E)
  • Change in electric potential (ΔV)
  • Change in distance (Δr)