Download Intro to Electric Circuits

Intro to Electric Circuits
GLAS wiring
Electric Circuits
• Electricity: The flow
of electrons. (Mobile
particles, carrying
charge)
• Circuit: A path for
electrons to flow in
http://chem-mgriep2.unl.edu/Courses/AnimatedAtoms.html
Voltage, current, and resistance
• The flow of electrons is like
the flow of water
• Driven by pressure (voltage)
• Pressure causes flow
(current)
• The relationship between
pressure and flow is set by
the obstacles (resistance) in
the flow path
• For the flow to do useful work
(have power), both pressure
and flow must be present
Hydroelectric Dam
ga.water.usgs.gov/edu/hyhowworks.html
Circuit functions
In general, circuits can be
thought of as
combinations of:
• Power Sources (battery,
generator)
• Loads (where power is
used) (lamps, speakers,
motors)
• Conduction Paths (wires)
• Controls (switches &
knobs)
• Indicators (meters,
flashing lights, buzzers)
Voltage
Voltage is the electrical
force, or "pressure",
that causes current to
flow in a circuit.
Voltage is the force that is
pushing the water (electrons)
forward.
It is measured in VOLTS
(V ).
Count Alessandro Volta (1745-1827)
Current
Current is the movement of
electrical charge - the flow
of electrons through the
electronic circuit.
In our analogy, current
would be the flow of water
moving through the tube
(wire).
Voltage
Current
Current is measured in
AMPERES (AMPS, A or I).
Current is defined to
flow from positive to
negative voltages
Andre-Marie Ampere (1775-1836)
Conductors, Insulators, and
Semiconductors
• A conductor is a material (usually a metal such as
copper) that allows electric current to pass easily.
• This is opposed to an insulator (plastic, glass) which
prevents the flow of electricity through it.
• Semiconductors have intermediate properties which
enable their conduction to be modified and controlled.
Resistance
Resistance is anything that
causes an opposition to the
flow of current in a circuit.
-
Voltage
+
Current
Resistance controls the amount of voltage
Resistance
and current in a circuit. Everything in a
circuit has a resistance (even wire). A
resistor is a device designed specifically to
have a constant resistance.
It is measured in OHMS (Ω).
Design and analysis of electronic circuits hinges on
thorough understanding of the relationships between
voltage, current, and resistance.
Quantification: Ohm’s Law
expresses the relationship
between current, voltage, and
resistance. It was named after
the German physicist Georg
Simon Ohm (1787-1854).
This is one of the most
fundamental concepts in
electronics. Learn Ohm’s
Law. Learn it inside and out!
Ω
Ohm’s Law
V is the voltage between two points (measured in volts)
I is the current flowing along a path between those two points
(measured in amperes)
R is the resistance of that path (measured in Ohms)
Volts = Amps times Ohms
Electronic Schematics
• Electronic circuits are drawn using schematics which use
standard symbols for each type of electronic component
Voltage
(Volts)
Circuit Schematic
I
Load/Resistor
(Ohms)
+
V -
R
CurrentCurrent
(Amps)
battery symbol
Diode
Transistors
resistor symbol
Capacitor
V?
If in this circuit we observe a
current flow of 12 amps (12A)
through the resistive load of 1
Ohm (1Ω), what must the
battery voltage be?
V=IR
V = 12 (Amps) x 1 (Ohm)
V = 12 Volts (12V)
I?
If we knew the battery was
supplying 12 volts, how do we
predict the current through a
resistive load of 1 Ohm?
I =V/R
I = 12 (Volts)/ 1 (Ohm) :
I = 12 Amps (12A)
If we knew the 12V battery
was supplying 12A of
current, what must the load
(resistance) be?
?Ω
R=V/I
R = 12 (Volts)/ 12 (Amps) :
R = 1 Ohm (1 Ω)
Electronic circuits
• For electrons to flow
contiusly, there must
be a compete circuit
in which electrons
return to their source.
• Think of it as a circle.
The paths may split
off here and there but
they always rejoin the
source eventually.
Condensation
Evaporation
http://www.ibiblio.org/kuphaldt/socratic/output/animation_switch_circuit_fast.gif
Series Circuit
A series circuit is one with all
the loads in a row. Like links
in a chain.
There is only ONE path for the
electricity to flow.
If this circuit was a string of
light bulbs, and one blew out
(became an open circuit), the
remaining bulbs would turn
off.
Circuit components in series experience the same current.
Parallel Circuit
A parallel circuit is one that has
two or more paths for the
electricity to flow – similar to a
fork in a river
In other words, the loads are
parallel to each other.
If the loads in this circuit were light
bulbs and one blew out, current would
still flow to the others.
Circuit components in parallel experience the same voltage.
Demonstration
Ohm’s Law test circuit
Current meter
(in series with load)
A
Voltage
source
V
Voltage meter
(in parallel with load)
Load
resistor