electric charge
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What Is Electric Charge?
In physics, electric charge is a fundamental property of certain subatomic
particles that is conserved and determines how these particles interact
electromagnetically. All electrically charged matter creates electromagnetic
fields and is influenced by them. If an electric charge is moving and
interacting with an electromagnetic field, an electromagnetic force is produced.
This resulting force is considered to be one of the four fundamental forces at
work in our universe. The SI unit for electric charge is the coulomb, named
after French physicist Charles-Augustin de Coulomb.
An electric charge on a body can be either positive or negative. Two bodies
with the same electric charge will be influenced by a mutually repulsive force
while two bodies with opposite charges will be influenced by a mutually
attractive force. Classical electrodynamics explains how charged bodies
interact, assuming one is working with bodies large enough to make quantum
effects negligible.
Throughout the twentieth century, many experiments have demonstrated that
electric charge is quantized. That is to say, electric charge is not distributed
along a continuum of possible charges that can be increased by any amount. In
fact, the minimum amount that can be added to an already existing electric
charge is the amount of the elementary charge, e, and it amounts to 1.602 x
10^{-19} coulombs. In an atom, the proton has a positive charge of e while the
electron has a charge of -e. The field of quantum electrodynamics is the study
of how these charged particles interact and are mediated by photons.
In everyday life, static electricity becomes a reality when you walk across a
carpet on a cold January morning only to get an annoying shock when you touch
the door handle. The shock you just received is an electrostatic discharge that
occurs because you are effectively building up a charge difference between
yourself and the door handle. The discharge occurs as a way of bringing the
total electric charge in the system back to equilibrium. Though one would think
that an electric current is flowing through oneself during this process, the
length of time of the discharge is too short for this to be true.
An electric current is a flow of charge across an electrically conductive
body of some kind. It is also taken to be the time derivative of charge, written
as:
I = dQ/dt
If one were to take the time integral of both sides of the above equation
with respect to a definite period of time, one would also be able to calculate
a total charge, Q, built up for that given timeby the integral:
Q = ∫ I dt
where the integral is the definite integral from t_{initial} to t_{final}. Such an equation might be used for determining the total charge built up
across the surface of a capacitor for a given current and time interval.