Download Current Electricity 1

ELECTRIC CURRENT
Electricity, like water, can only flow
if charged particles have potential.
An electron in motion defines an electric current.
eIn fact, any charged particle that moves defines an
electric current.
A moving sodium ion, for example, defines
an electric current
Na+
The rate of flow of electric charges is how we
measure current
e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e-
One coulomb of electric charges per second
passing through a conductor is 1 ampere, or 1
“amp”.
Remember…
1 Coulomb
1.6 x 10-19 C/e-
= 6.28 x 1018 electrons
So:
1 Coulomb/second = 6.28 x 1018 e-/s
1 amp = 6.28 x 1018 fundamental charges/sec
Current is abbreviated as:
I
What is the relationship between
potential and flow?
There is a direct relation between
potential and flow
So: I

V
But, some conductors allow for greater flow
than others.
So, the RESISTANCE (R) to flow must also
be considered.
We can say that resistance is INVERSELY
PROPORTIONAL to flow.
So: I

1
R
THEREFORE:
When we put everything together,
I
V
R
This equation is known as Ohm’s Law
In the world of electricity, the electrical
potential is the VOLTAGE (V)
It represents the energy per unit charge.
Remember that 1 Volt = 1 Joule/Coulomb
Unit summary:
Electrical potential =
current =
joule
coulomb
coulomb
sec
= volt
= amp
So, if
I
V then
R
R
V
I
volt
J /C J s J s

   2
R=
amp
C/s C C C
This unit is far more commonly known as the
OHM
=Ω
RESISTANCE
Depends on three factors:
1.The type of material (ρ)
2. The length of the conductor (L)
3. The cross-sectional area of the
conductor (A)
RESISTIVITY (ρ)
It varies with temperature
In general, the resistivity INCREASES with
increasing temperature
CIRCUITS
In order for electricity to be useful, it must
flow in a closed circuit.
The source of potential (voltage) must
have a closed pathway for current to flow.
With few exceptions, all circuits have
some resistance to current flow.
These symbols are
found in your
reference tables and
provide the standard
symbols for circuit
components.
These diagrams
represent circuits
found on Regents
Exams.
Can you identify the symbols?
TYPES OF CIRCUITS
There are two basic types:
Series
Parallel
A series circuit has all of the
resistors in line with the conductor
Parallel Circuits
Resistors are arranged in
parallel along more than one
conductor.
Series or parallel?
Series or parallel?
Note that the
ammeter is
placed in
series
Note that the
voltmeter is placed
in parallel.