Dynamic electricity consists of AC electric and DC electric . Dinamic electricity learn about current , voltage, resistance, electric circuit , Kirchoff law, ohm’s law, electris power, electric energy, transformer.
Many electric phenomena are around us.From the natural ones like lightinng and thunder to those generated by the power plants. Electricity in lightning and thunder are static electricity that is almost impossible to use. While the electricity from electric power plants is dynamic electricity that we can control and utilize it.
1. Electric Current
Electric current is defined as the rate of electric charges flowing through a conductor at any given time. If ΔQ is the charges flowing through a conductor of area a during the time Δt, then electric current ( I ) is defined
In SI the unit electric charges is coloumb ( C ), while the time unit is secomd ( s) . Hence, the unit for electric in SI is coulomb / second or C/s. This C/s was then given the name ampere ( A ) ,where 1A = 1 C/s . Electric current measured with amperemeter or ammeter. According to the convention , the direction of electric current is line with the direction of positive charges.It is known as the convention current. It was formulated before it was figured out that negatively-charged free electrons are actually free particles that move and generate electricity in conductor. The movements of these electrons are equivalent to those of positive charges flowing in opposite direction . Therefore , electrons move in opposite direction to the electric current.
Electric current is generated by electric current sources.It can be classified into direct current (DC) and alternating current(AC).Sources for direct current are batteries and accumulator, for instances. Whereas source for alternating current is electricity supplied by PLN and an alternating current generator, for example.
2.Electic Voltage
Electric voltage is often known as the electric potential difference,which is the potential difference of two terminals of an electric circuit.As with electric current, electric voltage cab be classified into DC voltage and AC voltage . Source for DC voltage are batteries and accumulators, for instances.Whereas sources for AC voltage are electricity supplied by PLN and AC generator , for example.
Why are the sources for DC current and DC voltage is same , and also for AC current and AC voltage ? What is the relantionship between electric current and voltage ? Electric current can also be generated if the voltage source is given a load (resistance). Therefore , a load electric voltage source of elerctric current . Electric current flow from higher potential to the lower potential. Electric voltage is measured by voltmeters. The SI unit for electric votage is volt (V)
B. Electric Resistance
1. Resistance of conducting wires
The resistance oe a conducting
wire ( R ) is proportional to its length ( l ) and inversely propotional to its
area ( A ) . Mathematically :
R=p.L/A
The unit of resistance in SI is
ohm . The quantity p is specific resistance or resistivity , the value of which depends on material of
conductor . The unit of specific resistance in SI is Ω .m .
An
instrument for measuring resistance is called an ohmmeter.
Simple ohmmeters cannot measure low resistances accurately because the
resistance of their measuring leads causes a voltage drop that interferes with
the measurement, so more accurate devices use four-terminal sensing.
Based on their conductivities , material can be classified
into three types; conductor , insulator , and semi conductors. Conductors are
material that transfer electric current very well.Conductor can be made of
metals such as iron, steel, alumunium , tin, and copper. Electric wires are
made of conductor materials.
Insulator are materials that transfer electric current
budly.Wood, rubber, ceramics, and plastic are insulator . Wire casting is made
of insulator . Semiconductors are materials that at room temperature behave as
insulators, but at high temperature behave as conductors. Some materials like
silicon and germanium have this propertiy.Semiconductor materials are used in
electric components like transistors and diodes
2.Resistor
Resistor are electronic component that function as
resistance for electric current.
a. Serial Circuit of Resistor
In a series configuration, the current through
all of the resistors is the same, but the voltage across each resistor will be
in proportion to its resistance. The potential difference (voltage) seen across
the network is the sum of those voltages, thus the total resistance can be
found as the sum of those resistances:
b. Parallel Circuit of Resistor
Resistors in a parallel configuration are each subject to
the same potential difference (voltage), however the currents through them add.
The conductances of the resistors then add to
determine the conductance of the network. Thus the equivalent resistance (Req)
of the network can be computed:
C. Ohm,s Law
Ohm's law states that the current
through a conductor between two points is directly proportional to the potential difference across the two
points. Introducing the constant of proportionality, the resistance one arrives at the usual
mathematical equation that describes this relationship:
V=I.R
where I is the
current through the conductor in units of amperes, V
is the potential difference measured across the conductor in units of volts, and R is the
resistance of the conductor in units of ohms. More specifically,
Ohm's law states that the R in this relation is constant, independent of
the current
The law was named after the
German physicist George Ohm, who, in a treatise published in
1827, described measurements of applied voltage and current through simple
electrical circuits containing various lengths of wire. He presented a slightly
more complex equation than the one above (see History section
below) to explain his experimental results. The above equation is the modern
form of Ohm's law.
D. Kirchoff’s law
Another physics who interested in the study of electric
circuit beside George Simon Ohm is Gustave Robert Kirchoff ( 1824-1887).
1. Kirchoff’s First law
The first kirchoff’s law
states that:
“The sum of the currents
flowing into a branch point isequel to the sum of the current flowing out of
that point”
In the picture to the
right, a junction of four conductors (wires) is shown. The currents i2
and i3 are flowing into the junction, while i1
and i4 flow out of it. In this example, Kirchhoff's Junction
Rule yields the following equation:
i2 + i3 = i1
+ i4
2. Kirchoff’s Second law
The kirchoff’s second law
states that :
“ The algebric sunm of the
electric potential difference ( voltage ) around any closed circuit must be
zero”
The formulation for
Kirchoff’s second law is :
∑V+∑IR = O
.
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