• When a mass with charge moves through an electric field, work is done
• The work done in moving a charge q is given by:

?W?=?q?V

• Where:
  • ?W?= change in work done (J)
  • q?= charge (C)
  • ?V?=?change in?electric potential?(J C-1)

   

• This change in work done is equal to the change in?electric potential energy?(E.P.E)
  • When?V?= 0, then the E.P.E = 0

   

• The change in E.P.E, or work done, for a point charge?q?at a distance?r1?from the centre of a larger charge?Q,?to a distance of?r2?further away can be written as:

• Where:
  • Q?= charge that is producing the electric field (C)
  • q?= charge that is moving in the electric field (C)
  • r1?=?first distance of?q?from the centre of?Q?(m)
  • r2?= second distance of?q?from the centre of?Q?(m)

   

Work is done when moving a point charge away from another charge

• Work is done when a positive charge in an electric field moves?against?the electric field lines or when a negative charge moves?with?the electric field lines

Step 1: Write down the known quantities

• • p.d. at?R,?V1?= 675 V
  • p.d. at?S,?V2?= 850 V
  • Charge,?q?= +3.0 nC = +3.0 × 10-9 C

Step 2: Write down the work done equation

W?=?qΔV

Step 3: Substitute in the values into the equation

W = (3.0 × 10-9) × (850 - 675) = 5.3 × 10-7?J

• 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 around a radial field or uniform field are perpendicular to the electric field lines

• 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