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

the reciprocal of resistance

units of mhos

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

resistors in series

[image]

R_T=R₁+R₂+R₃

I_T=V₁/R_T  I_T=I₁=I₂=I₃

V_R1=I_T*R₁ V_R2=I_T*R₂ V_R3=I_T*R₃

V_T=V_R1+V_R2+V_R3

C_EQ=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

[image]

R_EQ=1/[(1/R₁)+(1/R₂)]

V1=V_R1=V_R2

I_T=V1/R_EQ  I_T=I_R1+I_R2  Kirchoff- sums of the currents through each branch must be equal to the current entering the node from where the branches divide

I_R1=V_R1/R1  I_R2=V_R2/R2

C_T=C₁+C₂

L_EQ=1/[(1/L₁)+(1/L₂)]

voltage (V)*current (I)

units of watts

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

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

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

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)

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

X_c=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

X_L=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

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)+(X_L-X_C)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

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

V_s/V_p=N_s/N_p

V_s=secondary induced voltage

V_p=primary voltage

N_s and N_p= 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

I_p*V_p=I_s*V_s=P_p=P_s

resonant circuits have the ability to selectively amplify certain frequencies and not others

f_o=1/(2π√LC)

resonance in the vasculature is responsible for the peripheral arterial pressues having higher systolic pressure than the central pressure waveforms