Electric Field Strength

The electric field strength of a uniform field between two charged parallel plates is defined as:

$E = \frac{∆ V}{∆ d}$

Where:
- E = electric field strength (V m^-1)
- ΔV = potential difference between the plates (V)
- Δd = 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

Electric field between two plates, downloadable AS & A Level Physics revision notes

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

Two parallel metal plates are separated by 3.5 cm and have a potential difference of 7.9 kV.

Calculate the electric force acting on a stationary charged particle between the plates that has a charge of 2.6 × 10^-15 C.

Answer:

Step 1: Write down the known values

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

$E = \frac{∆ V}{∆ d}$

$E = \frac{7.9 \times 10^{3}}{3.5 \times 10^{- 2}} = 2.257 \times 10^{5} V m^{- 1}$

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

$F = q E$

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.)

Electric Field Strength (CIE A Level Physics)