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Introduction to DC circuits

Introduction to DC circuits . 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

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Introduction to DC circuits

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  1. Introduction to DC circuits A brief overview on the basics jbugni@nmu.edu

  2. 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

  3. 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

  4. The Atom cont. http://nasash.com/physics_thesaurus/wp-content/uploads/2008/06/a4atom.jpg

  5. 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.

  6. Example of basic circuit Switch Light bulb Conductor Battery http://phet.colorado.edu/simulations/sims.php?sim=Circuit_Construction_Kit_DC_Only

  7. 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

  8. 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

  9. 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

  10. Conductors • A solid, liquid or gas which electrons can easily pass through • Most commonly made from copper

  11. 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

  12. Electrical Symbols http://alldatapro.com/alldata/PRO~V156153136~C21290~R0~OD~N/0/41746505/42420070/42420075/42420077/34853741/34869956/34849309/144051240

  13. Example of Schematic http://alldatapro.com/alldata/PRO~V156153136~C21290~R0~OD~N/0/41746505/42420070/42420075/42420077/34853741/34869956/34869958/56473437

  14. 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 Ω

  15. Ohm’s law http://www.uakron.edu/groups/chemcar/docs/ohm.pdf

  16. 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 (Ω) • 12=4×R therefore R=12÷4=3 http://alldatapro.com/alldata/PRO~V155748232~C35580~R0~OD~N/0/80851247/83211660/83214935/83214937/34853741/34869214/34869215/34869322/34869325/146660096

  17. 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

  18. Series Circuit Schematic http://www.cybermike.net/reference/liec_book/DC/00090.jpg

  19. 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

  20. 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)

  21. Parallel Circuit Schematic http://www.faqs.org/docs/electric/DC/00083.png

  22. 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

  23. Series-Parallel Schematic http://www.faqs.org/docs/electric/DC/00123.png

  24. 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.

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