3-circuit Elements

ELECTRIC CIRCUITS THEORY 1 These lecture slides have been compiled by Mohammed LECTURE 3 SalahUdDin Ayubi. Circuit Elements 12 August 2005

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Outline • • • • •

Short Open Ideal voltage source Ideal current source Resistor

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Circuit Elements • Components that make up a circuit • The type of element determines either the voltage, the current, or the relationship between them

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Short V=0 I=?

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Open V=? I=0

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Ideal Voltage Source • Voltage is defined (regulated, controlled) by the element

DC (constant)

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Time-varying

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Ideal Voltage Source • Voltage is not dependent on current through element • Current through element is dependent on the rest of the circuit

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Ideal Current Source • Current is defined (regulated, controlled) by the element • Voltage across element is dependent on the rest of the circuit

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Resistor • Ohm’s Law v(t) = R i(t) V = IR • Units of resistance: ohms (Ω ) ∀ Ω = V/A • I = V/R = GV • G is conductance, units are siemens(S) = mhos( ) Ω 12 August 2005

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Resistance R = ρ L/A R = resistance ρ = resistivity of material L = length A = area

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Resistor Power • P = VI = V(V/R) = V2/R = I2R • E.g. power dissipated in 2k resistor is 250mW. Find I, V.

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Resistor Power • P = I 2R • I = √P/R = √250mW/2KΩ = 11.2mA V = IR = 11.2mA(2KΩ ) = 22.4V Check: 11.2mA(22.4V) = 250mW 12 August 2005

Engineer M S Ayubi

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Resistor Examples Find Vr, Ir, Pr

Find Pr

Find Vx

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Answers • Vr=10V, Ir=1A, Pr=10W • Pr=1mW • Vx=4V

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Equivalent Resistance • Series Req = R1 + R2 + R3

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Equivalent Resistance • Parallel Geq = G1 + G2 + G3

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1 Req = 1 1 1 + + R1 R2 R3

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Two Parallel Resistors Req =

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1 1 1 + R1 R2

=

R1 R2 R1 + R2

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Examples

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Examples

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Examples

Irreducible 12 August 2005

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