• The direction of electric fields is represented by?electric?field?lines
• Electric field lines are directed from positive to negative
  • Therefore, the field lines must be pointed?away?from the?positive?charge and?towards?the?negative?charge
  • Hence, field lines show the direction of force on a?positive test charge

   

Representing Radial Fields

• A radial field spreads out from a spherical charge in all directions
  • e.g. the field around a?point charge

   

• Around a?point charge, the electric field lines are directly radially inwards or outwards:
  • If the charge is?positive?(+), the field lines are radially?outwards
  • If the charge is?negative?(-), the field lines are radially?inwards

   

Radial electric field lines point away from a positive charge and point towards a negative charge

• This shares many similarities to radial gravitational field lines around a point mass
  • Since gravity is only?attractive, the field lines will look similar to the negative point charge, directed inward
  • However, electric field lines can be in?either?direction

• The?electric field strength?in a radial field follows an inverse square law
  • This means the field strength varies with distance?r?by 1 / r2

Representing Uniform Electric Fields

• A uniform electric field has the same electric field strength throughout the field
  • For example, the field between oppositely charged parallel plates

   

• This is represented by?equally spaced?field lines
  • This shares many similarities to uniform gravitational field lines on the surface of a planet

   

• A?non-uniform?electric field has varying electric field strength throughout
• The strength of an electric field is determined by the spacing of the field lines:
  • A?stronger?field is represented by the field lines?closer?together
  • A?weaker?field is represented by the field lines?further?apart

   

The electric field between two parallel plates is directed from the positive to the negative plate. A uniform E field has equally spaced field lines

• The electric field lines are directed from the?positive?to the?negative?plate
• The electric field strength in a?uniform?field is given by the equation?E?=?V?/?d
  • Hence,?E?proportional to the potential difference?V?between the plates
  • E?is inversely proportional to the distance?d?between the plates

Equipotential Diagrams

• Equipotential lines (2D) and surfaces (3D) join together points that have the?same?electric potential
• These are always:
  • Perpendicular?to the electric field lines in both radial and uniform fields
  • Represented by?dotted?lines (unlike field lines, which are solid lines with arrows)

   

• The potential gradient is defined by the?equipotential lines

Equipotential lines in a radial field are circles, showing lines of equal potential around a charge. They intersect radial field lines at 90°

Equipotential lines in a uniform field are straight lines. They too intersect uniform field lines at 90°

• Electric field lines around point charges are radially outwards for positive charges and radially inwards for negative charges
• The field lines must be drawn with arrows?from the positive charge to the negative charge

• In a?radial field?(eg. a point charge), the equipotential lines:
  • Are concentric circles around the charge
  • Become further apart further away from the charge

   

• In a?uniform field?(eg. between charged parallel plates), the equipotential lines are:
  • Horizontal straight lines
  • Parallel
  • Equally spaced

   

• No work is done?when moving along an equipotential line or surface
• Work is only done when moving?between?equipotential lines or surfaces
  • This means that an object travelling along an equipotential doesn't lose or gain energy and ΔV?=? 0