Resist. & Cap. Flashcards
Total voltage is equal to the _______ of the voltages across _______ _______ of the circuit.
Sum, all parts
Vt = V1 + V2 + V3
Current in each part is _______ to the current in _______ _______ part and _______ to total current.
Equal, every other, equal.
It = I1 = I2 = I3
In a purely inductive circuit (zero resistance) the current will _______ _______ the voltage by _______ _______.
Lag behind, 90 degrees
For resistance the voltage and the current are ________ ________.
For inductance the voltage and current are _____ _____ _____ _____ phase.
In phase, 90 degrees out of
In a purely inductive circuit no _______ is dissipated. Energy is stored in the ________ ________ and then returned to the circuit.
Power, magnetic field.
When Ohm’s law is applied to inductance, the relationship between voltage and current is called _______ instead of ________.
Reactance, resistance
The symbol for reactance is ______.
X
The symbol for inductance is ______.
L
The larger the inductance the larger the _______.
Reactance
The measurement for inductance is the ________.
Henry
In an AC circuit the higher the _______ the _______ the flux changes. This means that the reactance ________ as the frequency ________.
Frequency, faster.
Increases, increases.
The symbol for the factor 2πf is _____.
ω
The larger the capacitance, the _______ the reactance
Smaller.
The larger the frequency, the ________ the reactance.
Smaller
The formula to find capacitive reactance is:
Xc = 159,000 / f x C
What is the symbol we use to remind ourselves that voltage leads the current by 90 degrees?
j
The formula for adding voltages in a series AC circuit that are not in phase is:
Vt²=Vr²+Vc² _
To find total impedance in a series AC circuit the formula is:
Z² = R²+Xc² _
Or:
Z = √R² + Xc²
To find impedance by trigonometry, the formula is:
cos θ = a /h
Or:
cos θ = R/Z
To find power in an AC series circuit the formula is :
W = V x I x cos θ Or W = V x I x PF Or W = l²R
There is a circuit with a 5Ω resistor connected in series with a capacitor with a reactance of 12Ω @ a frequency of 60Hz. A series current of 1A produces a voltage drop of 5V across the resistor & 12V across the capacitor. What is the power factor (PF)?
PF = R / Z
PF = 5 / 13 = 0.3846
.03846 x 100% = 38.5% leading
There is a circuit with a 5Ω resistor connected in series with a capacitor with a reactance of 12Ω @ a frequency of 60Hz. A series current of 1A produces a voltage drop of 5V across the resistor & 12V across the capacitor. What is the power?
W = V x I x PF
W = 13 + 1 + 0.385 = 5W.
Check:
W = l²R = (1)² x 5 =5W
There is a circuit with a 5Ω resistor connected in series with a capacitor with a reactance of 12Ω @ a frequency of 60Hz. A series current of 1A produces a voltage drop of 5V across the resistor & 12V across the capacitor. What is the Vt?
Vt²=Vr²+Vc² Vt² = 5²+12² Vt² = 25 + 144 Vt² = 169 Vt² = √ 169 = 13
There is a circuit with a 5Ω resistor connected in series with a capacitor with a reactance of 12Ω @ a frequency of 60Hz. A series current of 1A produces a voltage drop of 5V across the resistor & 12V across the capacitor. What is the Z?
Z = √R² + Xc² Z= √5²+12² Z = √25+ 144 Z = √169 Z = 13Ω
There is a circuit with a 5Ω resistor connected in series with a capacitor with a reactance of 12Ω @ a frequency of 60Hz. A series current of 1A produces a voltage drop of 5V across the resistor & 12V across the capacitor. What is the phase angle?
cos θ = R / Z
θ = 5 / 3 = 0.3846
acos = 67
θ = 67° (approx)
A capacitance of 4 μF & a resistance of 30 Ω are connected in series across a 100V 1kHz ac source. Find Xc, Z, & It. Givens: C = 4 μF R = 30Ω V = 100V f = 1 kHz
Xc = 159,000 / f x C ⇒ 159,00 / 1000 x 4 ⇒ 159 / 4 = 40Ω (approx.)
Z = √R²+Xc² ⇒ √30²+40² ⇒ √900 + 1600 ⇒ √2500 = 50Ω
Vt = It x Z (same as V = IR) ⇒ 100 = It x 50 ⇒ It = 100/50 = 2A
A capacitance of 4 μF & a resistance of 30 Ω are connected in series across a 100V 1kHz ac source. Find Vr, Vc, & θ. Givens: C = 4 μF Χc = 40Ω R = 30Ω. Z = 50Ω V = 100V. It = 2A f = 1 kHz
Since It = Ir = Ic =2A. cos θ =R / Z = 30/50= .06000
Vr = Ir x Rr. acos 0.6000 = 53.13
Vr = 2 x 30 = 60V. θ = 53° (approx)
Vc = Ic x Xc
Vc = 2 x 40 = 80V
A capacitance of 4 μF & a resistance of 30 Ω are connected in series across a 100V 1kHz ac source. Find PF & W. Givens: C = 4 μF Χc = 40Ω R = 30Ω. Z = 50Ω Vt = 100V. It = 2A f = 1 kHz
PF = R/Z. W= V x I x PF = 100 x 2 x 0.6 = 120W PF = 30/50= 0.6000. Check: W = l²R = (2)² x 30 = 120W PF = 0.6000 x100 = 60% leading
In this series circuit, the total current of 2A leads the total voltage of 100V by 53°.
