# Introduction to DC circuits

Electronics - Devices

Oct 5, 2013 (4 years and 7 months ago)

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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
-

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

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

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

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Example of Schematic

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

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

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.