Transcript of Engineering Practice Electric Fitting Resistance Electrical resistance is the ratio of voltage drop...
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- Engineering Practice Electric Fitting
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- Resistance Electrical resistance is the ratio of voltage drop
across a resistor to current flow through the resistor. Polarities
are governed by the passive sign convention.
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- Current = voltage / resistance I = V / R V = I x R Definitions
Voltage = potential energy / unit charge, units = Volts Current =
charge flow rate, units = Amps Resistance = friction, units = Ohms
Example Voltage drop when current flows through resistor V 1 - V 2
= I R I R V1V1 V2V2 I, V & R
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- Power Consumed by Resistors Resistors consume power. v and i
are both positive or both negative.
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- Creating a Circuit Model A circuit model is usually two or more
circuit elements that are connected. A circuit model may have
active elements (sources) as well as passive elements (such as
resistors). By the assumption that electric signal propagation is
instantaneous in a circuit, our circuit model has lumped parameters
(A lumped system is one in which the dependent variables of
interest are a function of time alone. In general, this will mean
solving a set of ordinary differential equations (ODEs)).
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- Schematics Symbols represent circuit elements Lines are wires +
Battery Resistor Ground + V R I Sample circuit Ground voltage
defined = 0
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- Example of a Circuit Model
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- Kirchhoffs Voltage Law The sum of the voltage drops around a
closed path is zero. Example: -120 + V 1 + V 2 + V 3 + V 4 = 0
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- Kirchhoffs Current Law A node is a point where two or more
circuit elements are connected together. The sum of currents
associated with a node is zero.
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- Parallel And Series Resistors Series Same current flows through
all Parallel Same voltage across all + Note: these points are
connected together I V R1R1 R2R2 Series circuit V = R 1 I + R 2 I =
R eff I R eff = R 1 + R 2 Parallel circuit I = V/R 1 + V/R 2 = V/R
eff 1/R eff = 1/R 1 + 1/R 2 + V R1R1 R2R2 I1I1 I2I2 I
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- Resistive voltage divider Series resistor circuit Reduce input
voltage to desired level Advantages: simple and accurate complex
circuit can use single voltage source Disadvantage: dissipates
power easy to overload need R load