AC circuits Flashcards
In a parallel ac circuit with XL and
XC,
IL and IC are 180 out of phase.
What is the term for the out-of-phase
power associated with inductors and
capacitors?
Reactive power.
In an AC circuit, if the voltage and
current are in phase, the circuit is
resistive
For a capacitor in a sine-wave ac
circuit,
Vc lags ic by 90
ic leads Vc by 90
ic and Vc have the samefrequency.
Calculate the r.m.s. value of a
sinusoidal current of maximum value
20A.
14.14 A
Solution:
rms value 20A(0.707)
rms value 14.14 A Ans.
An alternating voltage is given by
v=75 sin (200πt −0.25) volts. Find
the phase angle (in degrees and
minutes)
14.32 (lagging)
In a parallel RL circuit,
IL lags IR by 90.
Calculate the current taken by a 10
F capacitor when connected to a
200 V, 100 Hz supply.
. 1.257 A
What is the power factor (PF) of a
purely resistive ac circuit?
1
A resistive and a capacitive load of
equal magnitude is connected in
series, determine the phase difference
between the voltage and the current.
current leads the voltage by 45°
For an inductor in a sine-wave ac
circuit,
VL leads iL by 90.
What will happen when the power
factor of a circuit is increased?
Active power increases
Calculate the capacitive reactance of a
capacitor of 20 μF when connected to
an a.c. circuit of frequency 20 Hz
397.9 ohms
The impedance in the study of
electronics is represented by resistance and ________.
reactance
In a series RLC circuit,
XL and XC are 180 out of phase.
A resistive and a capacitive load of
equal magnitude is connected in
series, determine the phase difference
between the voltage and the current.
current leads the voltage by 45°
In a series RC circuit,
Vc lags Vr by 90
An e.m.f. of 200 V at a frequency of
2 kHz is applied to a coil of pure
inductance 50 mH. Determine the
reactance of the coil and the current
flowing in the coil.
628 Ω; 0.318 A
If a circuit has an admittance of Y =
0.2 + j0.6, the circuit is
capacitive
What is the significance of
connecting loads in parallel?
It allows independent
operations of loads
What is the term used to identify an
AC voltage that would cause the
same heating in a resistor as a
corresponding value of DC voltage?
Root mean square (RMS).
When the frequency of the applied
voltage increases in a series RC
circuit,
ZT decreases.
In an ac circuit with only series
capacitors,
V 97.39sin 300 t 0.620 V
The voltages across three
components in a series circuit when
connected across an a.c. supply are:
Apparent power.
The product of the readings of an AC
voltmeter and AC ammeter is called:
150 – j100
A resistor of 150 Ω, a coil with
reactance 100 Ω and a capacitor with
reactance - 200 Ω are connected in
series. What is the complex
impedance R + jX?
VT lags IT by 90.
A value of –j500 represents
500 of capacitive reactance
.Inductive reactance, XL,
applies only to sine waves.
Susceptance, B, is the
reciprocal of reactance.
When the frequency of the applied
voltage decreases in a parallel RL
circuit,
18 Ohms
What is the total impedance of a
series AC circuit having a resistance
of 6 ohms, an inductive reactance of
17 ohms, and zero capacitive
reactance?
. ZEQ decreases.
An impedance draws a current i = 10
cos (ωt – 30degree) from a voltage, v =
220 sin (ωt + 30degree). What is the
impedance?
19.1 – j11.1
In a parallel RC circuit
IC leads IR by 90.
If a circuit has an admittance of Y =
0.5- j0.9, the circuit is
inductive
A coil, resistor and capacitor are in
parallel. The resistance is 1 Ω; the
capacitive susceptance is 1.0
siemens; the inductive susceptance is
- 1.0 siemens. Then the frequency is
cut to half its former value. What will
be the admittance vector, G + jB, at
the new frequency?
1 – j1.5
A branch current of +j250 mA
represents
250 mA of capacitive current.
What happens to reactive power in a
circuit that has both inductors and
capacitors?
15.92 µF; 0.25 A
A capacitor has a capacitive
reactance of 400 when connected
to a 100 V, 25 Hz supply. Determine
its capacitance and the current taken
from the supply.
It alternates between magnetic
and electric fields and is not
dissipated.
How do you compute true power
(power dissipated in the circuit) in a
circuit where AC voltage and current
are out of phase?
Multiply apparent power times
the power factor.
In a parallel RC circuit,
VA and IR are in phase.
An alternating voltage given by v =
100 sin 240t volts is applied across a
coil of resistance 32 and
inductance 100 mH. Determine the
circuit impedance.
40 ohms
What is a sine wave?
A wave whose amplitude at
any given instant can be
represented by the projection of
a point on a wheel rotating at
a uniform speed.
A 120 mH inductor has a 50 mA, 1
kHz alternating current flowing through it. Find the p.d. across the inductor
37.7 V
What type of wave is characterized
by a rise time significantly faster than
the fall time (or vice versa)?
Sawtooth wave.
What type of wave is made up of sine
waves of the fundamental frequency
and all the odd harmonics?
Square.
When the frequency of the applied
voltage increases in a parallel RC
circuit,
the phase angel, θ, increases.
ZEQ increases.
ZEQ decreases.
How many degrees are there in one
complete sine wave cycle?
360 degrees.
In a series RC circuit,
VR and I are in phase.
What is the description of a square
wave?
A wave that abruptly changes
back and forth that abruptly
changes back and forth
between two voltage levels and
stays at these levels for equal
amounts of time.
What type of wave is made up of sine
waves at the fundamental frequency
and all the harmonics?
Sawtooth wave.
