3.14: Resistive (R), Capacitive (C) and Inductive (L) Circuits Flashcards
- The difference between alternating current (ac) and direct current (dc) is
(a) ac changes value and dc does not
(b) ac changes direction and dc does not
(c) both (a) and (b) are incorrect.
(b) ac changes direction and dc does not
- When a sine wave has a frequency of 50 Hz, in 10 s it goes through
(a) 5 cycles
(b) 10 cycles
(c) 500 cycles
(c) 500 cycles
- If the peak value of a sine wave is 10 V, the peak-to-peak value is.
(a) 20V
(b) 5V
(c) IOV
(a) 20V
- In an AC circuit the effective voltage is:
(a) equal to the maximum instantaneous voltage
(b) greater than the maximum instantaneous voltage
(c) less than the maximum instantaneous voltage
(c) less than the maximum instantaneous voltage
Effective voltage is the rms voltage i.ie 0.707 peak voltage
Instantaneous voltage is v = VM sin 2πft
- Unless otherwise specified, any values given for current and voltage in an AC
circuit are assumed to be:
(a) average values
(b) instantaneous values
(c) effective values.
(c) effective values.
Effective values = RMS values
- If the peak value of a sine wave is 20 V, the RMS value is?
(a) 14.14V
(b) 6.37V
(c) 7.07 V
(a) 14.14V
- The average value of a 10 V peak sine wave over one complete cycle is
(a) 0 V
(b) 6.37 V
(c) 7.07 V
(b) 6.37 V
- The RMS value of a sine wave with a peak-to-peak value of 200 Volts is?
(a) 63.7 V
(b) 70.7 V
(c) 707 V
(b) 70.7 V
- In a pure capacitive AC circuit the average power
(a) 1/2 the peak power.
(b) .707 the RMS power
(c) Zero
(c) Zero
- If the frequency increases :
(a) Xc increases
(b) Xc decreases
(c) Xc stays the same
(b) Xc decreases
- If the frequency decreases :
(a) Xc increases
(b) Xc decreases
(c) Xc stays the same
(a) Xc increases
- If the frequency decreases :
(a) XL increases
(b) XL decreases
(c) XL stays the same
(b) XL decreases
- If the frequency increases :
(a) XL increases
(b) XL decreases
(c) XL stays the same
(a) XL increases
- If the frequency increases :
(a) R increases
(b) R decreases
(c) R stays the same
(c) R stays the same
- If the frequency increases :
(a) R increases
(b) R decreases
(c) R stays the same
(c) R stays the same
- Two series resistors are connected to an ac source. If there is 6.5 VRMS across
one resistor and 3.2 V RMS across the other, the peak source voltage is;
(a) 9.7V
(b) 9.19V
(c) 13.72V
(c) 13.72V
- In a series RC circuit, the voltage across the resistance is
(a) in phase with the source voltage
(b) lagging the source voltage by 90°
(c) in phase with the current
(c) in phase with the current
- In a series RC circuit, the voltage across the capacitor is
(a) in phase with the source voltage
(b) lagging the source voltage by 90°
(c) in phase with the current
(b) lagging the source voltage by 90°
- In a series RC circuit, 20 V RMS is measured across the resistor and 20 VRMS is
also measured across the capacitor. The RMS source voltage is;
(a) 20 V
(b) 28.28 V
(c) 40 V
(b) 28.28 V
- Whenever an AC frequency increases in a circuit, the Capacitive Reactance (Xc)
of components in the circuit will:
(a) Decrease
(b) Increase
(c) Remain the same
(a) Decrease
- A 3Ω resistor connected in series with a capacitive reactance Xc = 4Ω gives a
total impedance of :
(a) 7Ω
(b) 1Ω
(c) 5Ω
(c) 5Ω
- The frequency at which Inductive and Capacitive Reactance become equal is
known as the:
(a) Angular Frequency
(b) Resonant Frequency
(c) Reactive Frequency
(b) Resonant Frequency
- What is the reactance of a 0.002 microfarad capacitor a 1 kHz?
(a) 7.95 k ohms
(b) 79.5 ohms
(c) 795 ohms
(a) 7.95 k ohms
Dodgy answer but just know Reactance of a capacitor is calculated by:
- A 12Ω resistor connected in series with a capacitive reactance Xc = 5Ω gives a
total impedance of :
(a) 17Ω
(b) 14Ω
(c) 13Ω
(c) 13Ω
- In a capacitive circuit, the AC voltage and current relationship is such that the
voltage:
(a) Leads the current by 90 degrees
(b) Lags the current by 90 degrees
(c) Leads the current by 45 degrees
(b) Lags the current by 90 degrees
Capacitive circuit = voltage lags current by 90^
- In an inductor the voltage and current are:
(a) in phase
(b) the current leads the voltage by 90 degrees
(c) the current lags the voltage by 90 degrees
(c) the current lags the voltage by 90 degrees
- If a 7Ω resistor is placed in series with an Inductive reactance of 7Ω, the phase
angle of the total resultant voltage (referenced to the resistor) would be:
(a) 180 degrees
(b) 90 degrees
(c) 45 degrees
(c) 45 degrees
- A series tuned LC circuit shows which type of impedance at its resonant
frequency:
(a) Maximum
(b) Minimum
(c) Infinite
(b) Minimum
- In a parallel resonant tuned circuit the:
(a) Impedance is maximum
(b) External circuit current is maximum
(c) Voltage across L and C is higher than the supply voltage.
(a) Impedance is maximum
- When Xc = R the phase angle is;
(a) 0°
(b) 45°
(c) 90°
(b) 45°
- In a parallel RC circuit, there is 1 A RMS through the resistive branch and 1A RMS
through capacitive branch. The total RMS current is?
(a) 1A
(b) 2A
(c) 1.414A
(c) 1.414A
- A power factor of 1 indicates that the circuit phase angle is
(a) 0°
(b) 45°
(c) 90
(a) 0°
- For a certain load, the true power is IOO Watts the reactive power is IOO VAR.
The apparent power is;
(a) 200 VA
(b) IOO VA
(c) 141.4VA
(c) 141.4VA
- In an AC circuit energy sources are normally rated in;
(a) watts
(b) volt-amperes
(c) volt-amperes reactive
(b) volt-amperes
- To reduce the current in a series RL circuit, the frequency should be
(a) increased
(b) decreased
(c) constant
(a) increased
- When the frequency of an a.c. circuit containing resistance and inductance is
increased, the current :
(a) increases
(b) decreases
(c) stays the same
(b) decreases
- When a capacitor is connected to an a.c. supply, the current :
(a) leads the voltage by 180 degrees
(b) lags the voltage by 90 degrees
(c) leads the voltage by 90 degrees
(c) leads the voltage by 90 degrees
- When the resistor voltage in a series RL circuit becomes greater than the inductor
voltage, the phase angle
(a) Increases
(b) Decreases
(c) Is not affected
(b) Decreases
'’Becomes more resistive - more real power (or simply do with basic vector diagram)
- The total reactance of a series RLC circuit at resonance is
(a) Zero
(b) equal to the resistance
(c) infinity
(a) Zero
- The phase angle of a series RLC circuit at resonance is
(a) Zero
(b) 45°
(c) 90
(a) Zero
- In a series RLC circuit that is operating below the resonant frequency, the current
(a) is in phase with the applied voltage
(b) lags the applied voltage
(c) leads the applied voltage
(c) leads the applied voltage
'’When Xl = Xc at resonance Xl cancels Xc eg Z falls to zero and the current rises towards infinity. Below resonance Qc > Xl and at higher frequencies Xl > Xc
As above Xc is dominant i,e Current leads the voltage
- Two A.C. voltages are said to be in antiphase when:
(a) The are out of phase by 90°.
(b) The are out of phase by 180°.
(c) The are out of phase by 270°.
(b) The are out of phase by 180°.
- In an a.c. circuit where the voltage is 200V, the current is 100A and the power
factor is 0.5, the true power is :
(a) 10kW
(b) 20kW
(c) 200kW
(a) 10kW
Power factor = True power / Apparent Power
Apparent Power = Voltage * Current
(b) 4 W
Z=5, l=1, l squared R = 4 Watts
- What is the effect when voltage is changed from 28VDC to 28VAC on a resistor?
(a) A higher power output
(b) The same power output
(c) Lower power output
(b) The same power output
Assuming the 28 volts AC is RMS
- When calculating power in reactive or inductive AC circuits, the True Power is:
(a) more than Apparent Power
(b) more than Apparent Power in a reactive circuit and more than Apparent power in
an inductive circuit.
(c) less than Apparent Power
(c) less than Apparent Power
Pure capacitive AC circuit. What is the average power?
Pure capacitive AC circuit = Averagea power is zero
As Freqeuncy increases or decreases, what happens to Xc, XL and R?
Xc is the capacitive reactance and is a measure of the opposition to alternating current by the capacitor (measured in ohms
XL is inductive reactance and is the opposition to a changing current flow (ac) - measured in ohms
R (or Z) is the expression of the opposition that an electronic component, circuit, or system offers to alternating and/or direct electric current
In terms of Phases (in phase with current/voltage/lagging behind etc)
In a Series RC circuit
Volt across the resistance is …
Volt across the capacitor is …
What is meant by Resonant frequency?
What is the formula for RC total impedence?
In a capacative vs inductor circuit, is current and voltage in phase with each other?
When does minimum impedance occur in a LC circuit?
When does maximum impedance occur?
What is special about Xc = R?
What is the phase angle when there is a power factor of 1?
What is the relationship between current and frequency in a Series RL circuit?
Capacitor - What is the difference between current and voltage phase?
In a series RL circuit, what happens if you increase resistor volt?
What is the total reatance of a series RLC circuit at resonance?
What is the phase angle of an RLC circuit at resonance?
What is the relationship between current and voltage in an RLC circuit operating below resonant freq?
What happens when XL = Xc at resonance?
What is the relationship of Qc and XL below resonance?
If XL > Qc, what does this mean?
what angle is the Antiphase?
What is the relationship between True Power and Apparent Power?
