A Useful Definition.

**The electric field is a concept similar
to the gravitational field. In both, there exists a force acting from some
distance. This was not easy to accept for the ancient scientists.**

** The electric field idea was developed by
Michael Faraday. For him an electric field spreads outward from every charge
invading all the space. When a second charge is located near the first one,
it "feels" a force due to the electric field already present. That is, the
electric field in the place of the second charge interacts directly with that
charge to produce the force.**

** You can measure the electric field surrounding
a charge, a group of charges or a continuous distribution of charges, by measuring
the force on a small positive test charge. The test charge must be understood
as a very small positive charge not altering the rest of charges distribution
making up for the field to measure.**

** To make it more clear, assume a unique
positive charge Q. We want to measure its field through placing a test charge
q (positive and small) in the points a, b and c. **

**We know the forces are radially directed
out of Q and that its magnitudes are given by Coulomb's Law. The electric
field in the points a, b and c is defined in terms of the force over that
test charge.**

**The electric field E, in any point of the
space is defined as the force F exerted over a test charge in that point,
divided between the magnitude q of the test charge:
E = F / q
Let's notice this definition is similar to that of a gravitational field where
g is the gravitational field and F**

**With
this definition, the direction of the electric field at any point in the space
is defined as the direction of the force over a positive test charge placed
in that point. The magnitude of the electric field is the force per unit charge,
so E is measured in Newton/Coulomb (N / C).**

** Any electric field can be measured using
the above definition, whether dealing with a point charge or distributed charges.
A simple case is to calculate E at a distance r from a unique point charge
Q. As the magnitude of the force on the test charge is
F = (k q Q)/r ^{2}, is easy to demonstrate that the electric field
is **

** E
= F / q = k Q / r ^{2}.**

**Notice the electric field is independent
of q, the test charge. **

**Let's do an exercise for a better understanding
this: Calculate the magnitude and direction of the electric
field on a point P placed 20 cm to the right of a point charge Q = - 2.0 x
10 ^{-6} C.**

**Solution:
The magnitude of the electric field is:
E = k Q / r**

**Note: For a full scope of our homework physics
help, you can press our link for related sites named "Physics, Detailed
Homework Scope Help".**

**More
Electric Field Exercises, Press Here**

**Related Sites:**
**
· Physics, Main Page
· Physics, Mathematics
· Physics, Detailed Homework Scope Help
· Energy, Work and Power: Concepts
· Kinetic Energy
· Potential Energy
· Power
· Physics Problems, Example
· Physics Homework - Mechanical Energy Conservation Problems
· Physics Homework - Mechanical Power Problems
· Coulomb's Law
· Exercises Using Coulomb's Law
· Electric Potential Energy
· Exercises, Electric Potential Energy
· Ohm's Law, Principle
· Ohm's Law Exercises
· Gauss' Law
· Gauss' Law Exercises
· Second Newton's Law
· Second Newton's Law Examples, Part One
· Second Newton's Law Examples, Part Two
· Sound Waves
· Sound Waves: Standing, Interference, Doppler Effect - Examples
· Sound Waves, Doppler Effect - Examples
· Vectors, Scalars
· Vectors, Scalars - Analytic Method
· Addition Vector Tools, Problems
· **