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There are two devices that can be used to store or transfer electric charges, the electrophorus and the capacitor.
Electrophorus: an electrophorus consist of a metal disc fitted in
with
an insulating handle and another disc made of an insulating material.
Such as ebonite or polyethene. The insulating disc is first given a
negative charge, the metal disc is then placed on the insulating disc.
Positive and negative charges are induced on the metal disc. The metal
disc is then earthed, this allows for the excess electrons to flow from
the metal disc into the earth as they are repelled by negative
insulating disc. The metal disc is now left with excess positive
charges. The positive charges are stored in the metal disc and can be
transported by holding the electrophorus with its insulating handle. If
negative charges are required to be stored in the electrophorus, a
positive charge will need to be given to the insulating disc (material
of the disc can be changed from glass to perspex).
The capacitor:
A capacitor has two parallel plates separated by a short distance in a
di electric insulating medium. A capacitor is typically used for storing
charges in electric circuits.
Similar to mass modifying the space around it and setting up a
gravitational field, a charge modifies the space around it and sets up
an electric field. This field is known as a field of force then acts on
any other charge placed on it. It does so by exerting a force of
Electrostatics attraction on it. This force is repulsive for like
charges and attractive for unlike charges.
Current
For an Isolated charged conductor, the charges on the surface do not
move. In other words there are static charges, however if we provide a
conducting path the charges will flow the this happens we say an
electric current is produced. An electric current I is a measure of the
rate of flow of electric charge Q through a given cross section of a
conductor.
I=Q/t
The SI unit of current is the ampere (A). Since current is the rate of
flow of charge, we can say that a current of one ampere is the flow of
charge at the rate of 1 coulomb per second. A larger current of say 10
ampere will need 10 coulomb of charge to flow past a given cross section
of a conductor in one second. The size of the current such as 1ampere
or 10 ampere can be measured by means of an electric device called the
ammeter.
Electro motive force EMF
A source of electromotive force is a device in which non electrical
energy (chemical, mechanical or some other forms of energy) is converted
into electrical energy. Examples of sources of EMF include the battery,
thermocouple and the generator. The electromotive force EMF of a cell
is therefore defined as the energy converted from a non electrical form
to an electrical form where one coulomb of positive charges passes
through. EMF is the total work done in moving a unit positive charge
around the circuit.
E=W/Q where E is measured in volts V, W in Joules J, Q in Coulomb C.
The potential difference between two points is defined as the amount of
electrical energy converted to other forms when on coulomb of positive
charges passes between two points.
V=W/Q
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