• The magnitude of the electric field strength in a?uniform?field between two charged parallel plates is defined as:

• Where:
  • E?=?electric field strength?(V m-1)
  • V?= potential difference between the plates (V)
  • d?= separation between the plates (m)

   

• Note:?the electric field strength is now also defined by the units?V m-1
• The equation shows:
  • The greater the?voltage?between the plates, the?stronger?the field
  • The greater the?separation?between the plates, the?weaker?the field

   

• Remember this equation cannot be used to find the electric field strength around a?point charge?(since this would be a radial field)
• The direction of the electric field is from the plate connected to the?positive?terminal of the cell to the plate connected to the?negative?terminal

The E field strength between two charged parallel plates is the ratio of the potential difference and separation of the plates

• Note:?if one of the parallel plates is?earthed, it has a voltage of 0 V

Step 1: Write down the known values

• • Potential difference,?V?= 7.9 kV = 7.9 × 103?V
  • Distance between plates,?d?= 3.5 cm = 3.5 × 10-2?m
  • Charge,?Q?= 2.6 × 10-15?C

   

Step 2:?Calculate the electric field strength between the parallel plates

Step 3:?Write out the equation for electric force on a charged particle

F?=?QE

Step 4: Substitute electric field strength and charge into electric force equation

F?=?QE?= (2.6 × 10-15) × (2.257 × 105) = 5.87 × 10-10?N = 5.9 × 10-10?N (2 s.f.)

• When two points in an electric field have a different potential, there is a?potential difference?between them
  • To move a charge across that potential difference,?work?needs to be done
  • Two parallel plates with a potential difference ΔV?across them create a uniform electric field

   

• The electric field strength between the plates is given by the equations:

• Rearranging the fractions by multiplying by?Q?and?d?on both sides, gives:

Fd?=?ΔVQ

• When a charge?Q?moves from one plate to the other, its work done is

W?=?Fd

• Where:
  • W?= work done (J)
  • F?= force (N)
  • d?= distance (m)

   

The work done on the charge depends on the electric force and the distance between the plates

• Therefore, the work done in moving a charge?Q?through a potential difference ΔV?between parallel plates is also given by:

W?= ΔVQ