Fundamental Electrical Theory. Definitions Current (I): flow of electric charges per unit time or “flow rate”, measured in “amperes” or “amps” (A) Electromotive.

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Presentation transcript:

Fundamental Electrical Theory

Definitions Current (I): flow of electric charges per unit time or “flow rate”, measured in “amperes” or “amps” (A) Electromotive Force (emf) (E): a potential difference or “electric pressure” which drives the flow of charges, measured in “volts” (V) Resistance (R): an electrical circuit’s opposition to current flow, measured in “ohms” (  ) Conductor: a material which offers little resistance to current flow, e.g. silver, copper, iron, etc… Insulator: a material which offers high resistance to current flow, e.g. wood, paper, plastic, etc...

Direct Current (DC) Current flow is unidirectional and of constant magnitude (Batteries) Ohm’s Law: current in a circuit is directly proportional to the applied voltage and inversely proportional to the circuit resistance E = I R P = I E = I 2 R (W)

Basic Circuit Properties Electrons flow (-) to (+) Conventional Current flows (+) to (-) Kirchoff’s Law of Voltages (KVL) –Sum of all voltages in a complete circuit is zero –Choose arbitrary loop of a circuit (CW or CCW) –If encounters (+) terminal 1 st then (-), then its a voltage drop. (usually a resistor) –If encounters (-) terminal 1 st then (+) which is a voltage increase. (usually a battery) Sum of current into and out of a node is always zero and constant (KCL)

Basic Circuit Properties Series –Current is constant (constant flow rate of e - ) –Voltage drops across each resistor (pressure) –R = R 1 + R 2 + R 3 + etc Parallel –Voltage drop constant –I in = I 1 + I 2 + I 3 +etc –1/R = 1/ R 1 + 1/R 2 + 1/R 3 + etc

Example Problem #1 Determine V 1, V 2, V 3, V 4, and I. V1V1 V2V2 V4V4 V3V3 I 90V  55 10  Meters, volt-meter and amp-meter

Example Problem #2 Determine I 1, I 2, I 3, I 4 and total circuit resistance. I1I1 75V + - I4I4 I3I3 I2I2 20  30  20 

Batteries Dry-cell batteries: cylindrical zinc container, carbon electrode, and ammonium chloride/water electrolyte Wet-cell batteries: lead-acid battery is the most common, can be charged by forcibly changing the direction of electrical current

Voltage Kills It is the volume of the current that flows that kills amps = 1 milliamp Tingles 0.01 amps = 10 milliamps Severe shock, uncontrolled muscle spasms 0.1 amps = 100 milliamps DEATH! If the current passes through vital organs such as the heart.

FINSIHED FOR THE TIME BEING