Fundamentals of Electrical Circuits: Resistors, Capacitors, and Inductors, Study notes of Physics

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Introduction to Electricity

• Symbol: (q)
• Unit: Coulomb (C)
• The fundamental electric quantity is charge.
• Atoms are composed of charge carrying particles: electrons and protons , and neutral particles, neutrons.
• The smallest amount of charge that exists is carried by an electron and a proton.
• Charge in an electron: qe = - 1.602x
• 19 C
• Charge in a proton: qp = 1.602x10-^19 C

Charge

Current-Water Analogy

Voltage

• Potential difference across two terminals in a circuit “across variable.”
• In order to move charge from point A to point B, work needs to be done.
• Like potential energy at a water fall. - Let A be the lower potential/voltage terminal - Let B be the higher potential/voltage terminal o Then, voltage across A and B is the cost in energy required to move a unit positive charge from A to B.
• Symbol: V
• Unit: Volt

Voltage/Current-Water Analogy

Series Connection of Cells

• Each cell provides 1.5 V
• Two cells connected one after another, in series , provide 3 V, while three cells would provide 4.5 V
• Polarities matter

Wire-Water Analogy

Resistor Concept —I

• Flow of electric current through a conductor experiences a certain amount of

resistance.

• The resistance, expressed in ohms (, named after George ohm), kilo-ohms (k,

1000 ), or mega-ohms (M, 10

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) is a measure of how much a resistor resists

the flow of electricity.

• The magnitude of resistance is dictated by electric properties of the material and

material geometry.

• This behavior of materials is often used to control/limit electric current flow in

circuits.

• Henceforth, the conductors that exhibit the property of resisting current flow are

called resistors.

Resistor Symbols

Resistors-Water Analogy

Resistor V-I Characteristic

• In a typical resistor, a conducting element displays linear voltage-current

relationship. (i.e., current through a resistor is directly proportional to the

voltage across it).

I  V

• Using G as a constant of proportionality, we obtain:

I = GV

• Equivalently,

V = RI (or V = IR)

where R = 1/G.

• R is termed as the resistance of conductor (ohm, )
• G is termed as the conductance of conductor (mho, )

Resistors: Power Rating and Composition

• It is very important to be aware of power rating of resistor used in

circuits and to make sure that this limit is not violated. A higher power

rating resistor can dissipate more energy that a lower power rating

resistor.

• Resistors can be made of :
  • Carbon film (decomposition of carbon film on a ceramic core).
  • Carbon composition (carbon powder and glue-like binder).
  • Metal oxide (ceramic core coated with metal oxide).
  • Precision metal film.
  • High power wire wound.

Resistor Examples

Resistor

Contact leads

Symbol for resistor

Resistor Color Codes

Silver - x. White 9 X Grey 8 X Purple 7 X Blue 6 X Green 5 X Yellow 4 X Orange 3 X Red 2 X Brown 1 X Black 0 X Gold - x.

Band color Digit Multiplier

Gold 5%

Silver 10%

Red 2%

Brown 1%

Color Tolerance

None ±20%

Example

• The first band is yellow, so the first digit is 4
• The second band is violet, so the second digit is 7
• The third band is red, so the multiplier is
• Resistor value is (^47 105) %( )

  

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