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)
