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A circuit consists of electrical elements connected together in a closed path so that an electric current may flow continuously.
Electric Circuits -Introduction-
Current
Time rate of flow of charge past a given point
Charge
Quantity of electricity responsible for electric phenomena
i = dq/dt
Units: Ampere (A) : 1 coulomb per second
qExpressed in coulombs
Conventionally represented as the flow of positive charges. Complete description of current reqiures a value (negative or positive) and a direction.
Direct current (dc) = current of constant magnitude
Voltage
The work (energy) required to move a unit positive charge from the - terminal to the + terminal.
v= dw/dq
Power and Energy
Power: time rate of supplying or receiving power p= dw/dt
Units: Watts (w)
Unit: Volts (v)
pi= v * i
When current enters the + terminal and exits at the - terminal of voltage, voltage and current adhere to passive sign convention
Passive sign convention: power received (absorbed).Not: power supplied.
Circuit elements
A linear element satisfies the properties of both super position and homogeneity
if v1 is caused by i1and v2 is caused by i2 then i1+i2 results in v1+v2
Multiplying input by a constant = multiplying out put by a constant
Passive element = absorbs energy
Active element = supplies energy
Resistors
Ability to resist the flow of charge= resistivity, p
Resistance: property of an element that impedes the flow of current, represented by R
Ohms Law: v=Ri
R= Ohms= Ω = V/A
p = vi = v^2 / R = i^2 * R
Independent Sources
Source = voltage or current generator capable of supplying energy to a circuit
Independent = doesn't depend on other circuit variables
Voltmeter: measures voltage. Ideal: measures voltage from red to black probe ( + to -) and has terminal current = 0
Ammeter: measures current.Ideal: measures current through terminals and has 0 voltage.
= Open circuit
= Short circuit
Dependent Sources
Model the situation in which the voltage or current of one circuit element is proportional to the voltage or current of the second circuit element.
Represented by a diamond shape.
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