## Table of Contents

The electric field lines are parallel to the direction of force experienced by a positive test charge placed at that point.

## Basic Conventions When Drawing Field Lines

- Field lines extend
**out**from**positive**charges - Field lines go
**into****negative**charges - All field lines are continuous curves or lines without breaks
- Field lines
**never**touch or cross each other’s path - Field lines in the same direction tend to stay as far apart as possible
- Field lines in the opposite direction tend to cancel each other
- When electric field strength E increases (i.e. charge is stronger), the number of field lines increase. (i.e. the closer the field lines, the stronger the electric field strength)
- Field lines are always perpendicular from its source
- Stronger field lines retain their shape better therefore are less distorted by other charges around

**When 2 or more charges are placed in the vicinity of each other, the resultant E-field shape will be a combination of the individual E-field.**

- When both point charges are of the same magnitude, the shape will be symmetrical
- When both point charges are of different magnitude, the shape will be asymmetrical

## Electric Field Lines From A Positively Charged Sphere

## Electric Field Lines From One Positively Charged Sphere And One Negatively Charged Sphere

## What Does It Mean By Uniform Electric Field?

An uniform electric field is defined as an electric field whose influence over a charge is constant regardless of the point of the space taken into consideration.

An electric field generated by a point charge is not uniform because the electric field lines are spaced further apart as the distance from the charge increases. (The electric field gets weaker.)

Almost uniform E-field can be obtained with oppositely charged parallel plates when the length of the plates is much longer than the distance between them.

This means that wherever a charged particle is placed between those plates, it experiences the same magnitude force, in the same direction.

### Electric Field Strength Between Plates

The electric field strength between the oppositely charged parallel plates is given by:

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

, where

- $\Delta V$ is the potential difference between the two parallel plates
- $\Delta d$ is the distance between the plates

From this, you know that a uniform field is expressed in terms of the change in electric potential per unit charge.

## Electric Field Strength Due To Double And Multiple Point Charges In Space

$E_{y} = E_{1y} + E_{2y}$

$E_{x} = E_{1x} + E_{2x}$

$E = \sqrt{E_{x}^{2} + E_{y}^{2}}$

### Procedure:

- Resolve the electric field vectors into x and y components
- The x and y components of the resultant electric field can be found using the first two equations above
- The resultant electric field is then computed using the third equation

**Note:** If you are familiar with vectors, the resultant electric field at a point is just the vector sum of the two or more electric fields due to the charges.