18.2 Uniform Electric Fields

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1. What is a Uniform Electric Field?

An electric field is a region in space where a charged particle experiences a force. You can picture it using field lines — imaginary arrows that show the direction of the force on a small positive charge placed in that region.

A uniform electric field is one where the field strength is the same at every point. This means a charged particle placed anywhere in the field experiences exactly the same force, no matter where it is.

You can create a uniform electric field by connecting two flat, parallel metal plates to a power supply (a battery or DC source). One plate becomes positively charged and the other becomes negatively charged. The electric field between them is uniform — the field lines are straight, parallel, and evenly spaced.

2. Electric Field Strength Between Parallel Plates

Electric field strength (E) tells you how strong the electric force is at a point. It is defined as the force per unit positive charge:

$E = \frac{F}{q}$

Where:

• E = electric field strength (unit: N C⁻¹ or V m⁻¹ — these are equivalent)
• F = force on the charge (N)
• q = the charge (C)

For a uniform field between parallel plates, there is a simpler and very useful equation:

$\boxed{E = \frac{\Delta V}{\Delta d}}$

Where:

• E = electric field strength (V m⁻¹)
• ΔV = the potential difference between the plates (V) — this is the voltage of the power supply
• Δd = the distance (separation) between the plates (m)