Introduction to DC circuits

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5 Οκτ 2013 (πριν από 3 χρόνια και 10 μήνες)

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A brief overview on the basics

jbugni@nmu.edu

The Atom


Basic unit of matter


Made up of tiny particles, two are important in
electricity


Protons


Contained in the nucleus (center) of the atom


Have a positive charge


Electrons


Move around the nucleus in paths called shells


Have a negative charge


Electrons in the outer most shell are called valence electrons

The Atom cont.


Amount of negative charge of each electron is equal to the
amount of positive charge of each proton


If enough energy is applied to an atom, some valence
electrons will leave the atom


Ions


Charge atom


Negative ion has more electrons than protons


Positive ion has more protons than electrons


Ions with similar charges repel, different charges attract


Current flows when electrons move from one atom to
another


The Atom cont.

http://nasash.com/physics_thesaurus/wp
-
content/uploads/2008/06/a4atom.jpg

What is a circuit?


Defined as a system of conductors and devices through
which electrons can move.


Consists of three characteristics


Must contain a power source


Complete path for current flow from one side of the
power source to the other


Contains some type of resistance to limit the amount of
current.

Example of basic circuit

Light bulb

Switch

Conductor

Battery

http://phet.colorado.edu/simulations/sims.php?sim=Circuit_Construction_Kit_
DC_Only

Voltage


Measured in volts


Electrical pressure used to move electrons throughout
the circuit


Also defined as the potential difference between two
unlike charges


Think of voltage as the water pressure in a garden hose

Current


Measured in amps or ampere


Movement of electrons through the circuit


Think of the water flow in the garden hose


DC refers to direct current or movement of electrons in
one direction

Resistance


Measured in ohms


Opposes the movement of current


Reduces the amount of current in a circuit


Think of kinking the garden hose


May also be referred to the load of the circuit

Conductors


A solid, liquid or gas which electrons can easily pass
through


Most commonly made from copper


Schematic Diagrams


Standard way of communicating information in
electricity and electronics


Components are shown by graphic symbols


May not accurately represent the actual location of
components



Electrical Symbols

http://alldatapro.com/alldata/PRO~V156153136~C21290~R0~OD~N/0/41746505/42420070/42420075/42420077/34853741/34869956/34849309/
144
051240

Example of Schematic

http://alldatapro.com/alldata/PRO~V156153136~C21290~R0~OD~N/0/41746505/42420070/42420075/42420077/34853741/34869956/34869958/
564
73437

Ohm’s law


Discovered by German physicist Georg Simon Ohm


Shows the relationship of resistance (R), current (I) and
voltage (E) along with power (W)


The most common equation is E=IR, where voltage is equal
to resistance times current


Basis for all study of electrical properties




Ohm’s law

http://www.uakron.edu/groups/chemcar/docs/ohm.pdf

E=IR


For example: If a circuit has a constant power source
of 12 volts and 4 amps of current, the resistance of the
circuit must be 3 ohms (

)


12=4
×
R therefore R=12
÷
4=3

http://alldatapro.com/alldata/PRO~V155748232~C35580~R0~OD~N/0/80851247/83211660/83214935/83214937/34853741/34869214/34869215/
348
69322/34869325/146660096

Series Circuit


Only one path for current to flow


Total resistance of circuit is the sum of all resistances


Current is consistent throughout the circuit


Total voltage is spread across the loads in the circuit


Voltage drop is amount of voltage required to force the
current through the load or resistance


Sum of all the voltage drops equals the total voltage
applied to the circuit


Series Circuit Schematic

http://www.cybermike.net/reference/liec_book/DC/00090.jpg

Parallel Circuit


Contain multiple connections or branches


Loads operate independently


Total current is divided between the branches


Determined by the resistance of the branch


Calculated by Ohm’s law


Voltage is the same on all the branches


Total resistance decreases as more branches are added


Always less than the branch with lowest resistance

Parallel Circuit cont.


Resistance formulas


Two resistances of unequal value


RT=(R1
×

R2)
÷
(R1 + R2)


All resistances are equal in value


RT = (value of one resistance)
÷

(number of resistances)


If resistances are not all equal in value


RT = 1
÷

(1/R1 + 1/R2 + 1/R3 + … + 1/RN)



Parallel Circuit Schematic

http://www.faqs.org/docs/electric/DC/00083.png

Series
-
Parallel Circuit


Combination of both series and parallel circuits


Requires formulas from both series and parallel
circuits to calculate resistance, current and voltage
drops


Most electrical devices have series
-
parallel circuits

Series
-
Parallel Schematic

http://www.faqs.org/docs/electric/DC/00123.png

Other sources


Buban, P., Schmitt, M. L., & Carter Jr., C. G. (1992).
Understanding Electricity and Electronics Technology.

Peoria: Macmillan/McGraw
-
Hill.


Grob, B. (1992).
Grob Basic Electronics.

Westerville:
Macmillan/McGraw
-
Hill.