circuits Flashcards
what is a series circuit
a circuit with only one current path
what is a parallel circuit
a circuit that has more than one current path connected to a common voltage source
what circuit can kirchkoffs law be applied to
series circuits
what is kirchkoffs law
the sum of all the voltage drops around a single closed circuit is equal to the total source voltage in a closed path
Vs = VR1 + VR2 + VR3…
what is a voltage drop
a drop in voltage due to the current in circuit running through a resistor
what is the voltage divider rule
the voltage drops acroos any given resistor in a SERIES circuit = (single resitor : total resistance) x Source voltage
(R1 / R1+R2…) x Vs = voltage drops
what is total resistance in parallel circuits
the reciprocal of the sum of reciprocal of each resistor
1/R1 + 1/R2 +1/R3 … = 1/RT
what is an RC circuit
a circuit that has resistors and capacitors
what are capacitors
can store charge and act as a temporary battery
what is capacitance
the ability to store charge
- unit farad (F)
how to calculate capacitance
ratio of charge to voltage
C = Q/V
what factors affect how much charge a capacitor can have
- size of the capacitor
- voltage
how does a capacitor work in a series circuit
when connected in series, total capacitance is smaller than the smallest.
1/CT = 1/c1+1/c2+1/c3…1/cn
CT = 1 / (1/c1+1/c2+1/c3…1/cn)
how does a capacitor work in a parallel circuit
when connected in parallel, total capacitance is the sum of the individual capacitors
CT = c1 + c2 +c3 …
how does a capacitor work in a DC circuit
when current is run through a DC source within a series circuit, the changing current is exponential
- discharge of current is also exponential
what is the general voltage formula when a capacitor is involved within the circuit
v = vF + (Vi - VF)e^-t/RC
v - instantaneous voltage value
VF= final voltage
Vi= initial voltage
t = time
R = resistance
C = capacitance
how does final Capacitor voltage change during charging & discharging
when the capacitor is charging, VF > Vi
when discharging, VF < Vi
how does a capacitor work in an AC circuit
the instantaneous capacitance current is equal to the capacitance x the instantaneous rate of change in voltage across the capacitor
i = c x dv/dt
dv/dt = derivative of v with respect to time
what is a phase shift
when a sine wave is applied through a capacitor, current leads voltage with a phase angle of 90º
what is capacitive reactance
opposition to a sinusoidal current, in ohms
Xc = 1 / (2x3.14 xf x c)
what is reactive power
the rate at which a capacitor stores or returns energy
- unit = VAR ( voltage-ampere reactive)
how do you calculate reactive power
Pr = Vrms x Irms
= V^2rms / Xc
= I^2rms x Xc
In a RC series circuit, how is voltage and current effected
the phase angle between volatge and current is between 90º and 0º dependent on values of reactance and resistance
how to calculate phase angle
tan -1 (Vc/Vr)
what is impedence
total opposition to sinusoidal current (ohms)
what is an RL circuit
a circuit that has resistors and Inductors
what are ohms laws for series RC circuits
Using phasor qunatities:
V = IZ
I = V/Z
Z = V/ I
what happens to the energy in a purely resistive AC circuit
true power : all energy delivered by the source is dissipated. in the form of heat by the resistance
Ptrue = i^2 x R
what is true power
the power in the resistor that does work (watts)
what happens to the energy in a purely capacitive AC circuit
Reactive Power : all energy is stored by the capacitor during a portion of the voltage cycle, before it is then returned to the source during another portion of the cycle
- no conversion of energy to heat
Pr = I^2 x XC
what is reactive power
power within the capacitor
- unit (VAR)
what happens to the energy in a RC AC circuit
Apparent power : energy is alternately stored & returned by the capacitance AND some energy is dissipated by the resistance during each alteration
Pa = VI = I^2 x V
what is apparent power
total power that appears to be transferred between the sources & the RC circuit
what is the relationship between apparent and true power
Ptrue = PaCos()
PF = cos ()
1= purely reactive
0 = purely resistive
what is self inductance
the coils ability to establish an induced voltage as a result of a change in current
how does an inductor impact a series circuit
total inductance is the sum of individual inductances
how does an inductor impact a parallel circuit
total inductance is smaller than the smallest one
LT = 1 / ( 1/L1 + 1/L2 +1/L3 …)
how does an inductor impact a DC series circuit
current change is exponential
what is a time constant
how long it takes the component to charge / discharge
how to calculate RC circuit time constant
R x C
how to calculate RL circuit time constant
L / R
what is the general current formula when an inductor is involved in the circuit
IF + ( Ii - IF)e^-rt/L
IF = final current
Ii = initial current
R= resistance
t = time
L = inductance
how is current effected when the inductive field is building / collapsing
when the inductive field is building, IF > Ii
when the inductive field is collapsing, IF < Ii
what is inductive reactance
an opposition to sinusoidal current by an inductor (XL)
- unit ohms
In a RL circuit, how is voltage and current effected
when a sine wave is applied to an inductor, the phase shift between current & voltage is always 90º
how is power effected by the inductor in a RL circuit
small amount of power is dissipated in winding resistance
Ptrue = (Irms)^2 x Rw
reactive power in a RL circuit is..?
the rate at which the inductor stores & returns energy
Pr = Vrms x Irms
= (Irms)^2 x XL
- unit VAR
what is quality factor in an RL circuit
how efficiently the coil stores energy
- the ratio of energy stored to energy lost
what is impedance in an RL circuit
phasor sum of R and jXL
XL - inductive reactive
R - +ve x axis
J - +ve y axis
what is an RLC circuit
when resistors, capacitors and inductors are all connected in series
what is resonance
a circuit is purely resistive
- frequency is XC = XL
- current is at its maximum
- total impedance is minimum Z = R
