Current Electricity

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Current Electricity
Main parts to any circuit
Battery
Switch
Conducting Wire
Lamp
Resistor
A Circuit Diagram
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Anatomy of a Circuit
Dry Cell - Power for the circuit (a chemical
reaction that produces
electricity from a paste).
Battery - a combination of cells
Switch - Opens and closes the circuit (a closed
path for the charge to flow)
Resistor - represents a load which converts
electrical energy into other
forms of energy. They all resist the movement
of charge through the circuit.
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Batteries provide energy to push negative charges
through a circuit. This movement is called
current.
Current The amount of charge that passes a
point in a conducting wire every second. Charge
is measured in a unit called Coulombs (Q)
current charge moving past a point
time

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Movement of charge in a battery occurs due to
repulsion and attractive forces
Charge travels from negative terminal to positive
terminal through a conductor. Electrons are
attracted to the positive so they can flow
through the circuit.
Break the circuit - (i.e. a switch) and the
charge can no longer flow
This current is measured by an AMMETER
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In a circuit, the movement of electrons is
continuous and controlled
Excess electrons accumulate at one terminal of
the battery (making it negative). These
electrons withdraw from the positive terminal
leaving it positive.
This electrical energy stored in the battery is
called electrical potential energy - the
electrons have the potential to do work by will
not do so until the circuit is closed.
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When describing electrons in a circuit we
describe their energy as a function of their
charge
J/C
We can also compare the J/C of one point in the
circuit to another. This is called the
POTENTIAL DIFFERENCE (i.e. the difference in
potential energy between two points) and measured
by the Volt.
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Typical Circuit
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Resistance
Resistance - hinders motion of charge and
converts electrical energy into other
forms of energy.
Resistance is defined in Ohms (?) The ratio of
the potential difference across the load (V) to
the current through the load (I)
V
R

or in units...
I
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Resistance is named after Georg Ohm (1798-1854)
who discovered Ohms Law
V IR
Any electrical device that has a constant
resistance regardless of the potential difference
is called an OHMIC resistor. Most appliances are
not though as their resistance changes as the
potential difference changes
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Materials in a circuit
Understanding the characteristics of conducting
materials allow electrical engineers to design
efficient resistors and conductors
Resistance increases with length proportionally.
Resistance decreases with area proportionally.
As temperature increases - resistance increases.
Due to atomic structure, some metals allow
electrons to flow more easily than others.
Some resistors are made of poor conductors
(Graphite) while other are just long thin wires
which are coiled to reduce their size
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Conducting wires that carry large currents have
large wires to minimize resistance.