# Shared Flashcard Set

## Details

lecture 5
electrical circuits and physiologic analogs AA students
17
Physics
09/06/2010

Term
 resistance of a wire
Definition
 R=(L/A)*ρ   R=resistance L=length (m) A=cross sectional area (m2) ρ=resistivity of the material (copper 1.62*10-8 ohm m)   as length and resistivity increase the resistance increases as the cross sectional area increases the resistance decreases
Term
 relationship between voltage and current in a resistor of constant value
Definition
 slope is the resistance
Term
 conductance
Definition
 the reciprocal of resistance   units of mhos
Term
 resistor
Definition
 provides some opposition to the flow of electric current   as current [I(t)] flows through the resistor is produces a voltage drop across the resistor [v(t)], commonly called a voltage drop   relationship btwn voltage drop and the current flow is given by Ohm's law: v(t)=i(t)*R   the voltage drop is proportional to the current flow
Term
 resistors in series
Definition
 [image]                         RT=R1+R2+R3 IT=V1/RT  IT=I1=I2=I3 VR1=IT*R1 VR2=IT*R2 VR3=IT*R3 VT=VR1+VR2+VR3 CEQ=1/[(1/c1)+(1/c2)+(1/c3)] L=L1+L2+L3   Kirchoff- the sums of the voltage drops around the "loop" must be equal to the applied voltage V1
Term
 parallel circuit
Definition
 [image] REQ=1/[(1/R1)+(1/R2)] V1=VR1=VR2 IT=V1/REQ  IT=IR1+IR2  Kirchoff- sums of the currents through each branch must be equal to the current entering the node from where the branches divide IR1=VR1/R1  IR2=VR2/R2 CT=C1+C2 LEQ=1/[(1/L1)+(1/L2)]
Term
 electrical power
Definition
 voltage (V)*current (I) units of watts
Term
 capacitor
Definition
 an energy storage device constructed of 2 conducting plates separated by an insulating (dielectric) material with no electrically conductive connection btwn the plates   stores electrical energy by separating charges (coulombs) such that one plate becomes + and the other -   the separation of charges created by the movement of electrons results in the creation of an electrostatic field.  This stores electrical potential energy that can be released back into the circuit whenever it is required   C=(K*A)/d C=capacitance in farads K=dielectric constant of the material separating the plates A=cross sectional area of the plates d=distance btwn plates
Term
 inductor
Definition
 a coil of wire that is an electrial energy storage device   an electromagnetic field is produced  that is proportional to the magnitude of the current when a current moves thru the wire   electrical energy is stored in the inductor as an electromagnetic field   inductance is physically proportional to the cross sectional area of the coil of wire, number of turns of wire in the coil, and the length of wire making up the coil   units: Henry
Term
 diode
Definition
 a semiconductor device which only permits current to flow in one direction   conventional current flows in the direction of the arrow on the schematic symbol of the diode   the AC source provides a sine wave signal. while the sine wave is in the positive half of the cycle conventional current flows fromt he plus sign on V1 through the circuit to the other terminal of V1. during the negative half of the cycle, no current will flow bc the positive side of V1 is at the bottom and conventional current can't flow in the reverse direction through the diode
Term
 switch
Definition
 device that opens the circuit by interrupting the wire through wich current flows   when the switch is closed the circuit is again complete and the switch acts like an ideal piece of wire (0 resistance)
Term
 time constant
Definition
 τ=R*C   when a resistor is placed between the battery and the capacitor it limits the maximum current flow and therefore determines how quickly the capacitor becomes charged   as the resistance increases the time required to complete the flow of electrons on to and off of their respective plate's increases
Term
 capacitive reactance
Definition
 Xc=1/(2πfC)   f=frequency of the current in Hz C is the capacitance in Farads   as the frequency increases the capacitive reactance goes down and more current is permitted to flow in the circuit   as capacitance increases so does the current flow if the frequency is held constant   ex: patient on an operating table
Term
 inductive reactance
Definition
 XL=2πfL   f=frequency in Hz L is the inductance in Henries   as the frquency increases the inductive reactance increases and less current is permitted to flow   if the inductance increases the reactance increases and the current flow decreases
Term
 impedance (Z)
Definition
 used to describe the opposition to the flow of current in time varying circuits   resistance is a component of impedance, which is also made up of capacitive and inductive reactance   systemic vascular resistance is used as a gross simpification of vascular impedance   Z=√(R2)+(XL-XC)2   also associated with a phase angle that ultimately describes the relationship(time delay) btwn the voltage and the current in the circuit Φ=tan ((XL/XC)/R
Term
 transformer
Definition
 device that transfers electrical energy from one circuit to another without a physical connection (wire) btwn them   a changing (alternating) current in the primary, or first circuit, creates a changing magnetic field due to the alternating electrical current flowing thru it; in turn, this magnetic field induces a changing voltage in the secondary or second circuit   Vs/Vp=Ns/Np Vs=secondary induced voltage Vp=primary voltage Ns and Np= number of turns of wire in their respective windings     the power in the primary circuit is approx. equal to the power in the secondary circuit Ip*Vp=Is*Vs=Pp=Ps
Term
 Resonance
Definition
 resonant circuits have the ability to selectively amplify certain frequencies and not others fo=1/(2π√LC)   resonance in the vasculature is responsible for the peripheral arterial pressues having higher systolic pressure than the central pressure waveforms
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