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Introduction to DC circuits . A brief overview on the basics. 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

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introduction to dc circuits

Introduction to DC circuits

A brief overview on the basics

the atom
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
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 cont1
The Atom cont.

what is a circuit
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
Example of basic circuit


Light bulb



  • 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
  • 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
  • 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
  • A solid, liquid or gas which electrons can easily pass through
  • Most commonly made from copper
schematic diagrams
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
Electrical Symbols

example of schematic
Example of Schematic

ohm s law
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 law1
Ohm’s law

  • 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 (Ω)
  • 12=4×R therefore R=12÷4=3

series circuit
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
Series Circuit Schematic

parallel circuit
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
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
Parallel Circuit Schematic

series parallel circuit
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
Series-Parallel Schematic

other sources
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.