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Alternating Currents Online MCQs with Answers
What is the frequency of alternating current in most household electrical systems?
a) 50 Hz
b) 60 Hz
c) 50 kHz
d) 60 kHz
The voltage and current in an AC circuit:
a) Are always in phase
b) Are always out of phase
c) Can be in phase or out of phase depending on the circuit
d) None of the above
In an AC circuit, the peak value of voltage is 100 V. What is the RMS value of voltage?
a) 50 V
b) 70.7 V
c) 100 V
d) 141.4 V
The peak value of current in an AC circuit is 10 A. What is the RMS value of current?
a) 5 A
b) 7.07 A
c) 10 A
d) 14.14 A
What is the relationship between the peak value and RMS value of voltage or current in an AC circuit?
a) Peak value = 2 * RMS value
b) Peak value = RMS value / √2
c) RMS value = Peak value / √2
d) RMS value = 2 * Peak value
What is the phase difference between voltage and current in a purely resistive AC circuit?
a) 0 degrees
b) 45 degrees
c) 90 degrees
d) 180 degrees
What is the phase difference between voltage and current in a purely inductive AC circuit?
a) 0 degrees
b) 45 degrees
c) 90 degrees
d) 180 degrees
What is the phase difference between voltage and current in a purely capacitive AC circuit?
a) 0 degrees
b) 45 degrees
c) 90 degrees
d) 180 degrees
What is the power factor of a purely resistive AC circuit?
a) 0
b) 0.5
c) 1
d) It depends on the frequency of the AC
What is the power factor of a purely inductive AC circuit?
a) 0
b) 0.5
c) 1
d) It depends on the frequency of the AC
What is the power factor of a purely capacitive AC circuit?
a) 0
b) 0.5
c) 1
d) It depends on the frequency of the AC
What is the formula for calculating the power in an AC circuit?
a) Power = Voltage * Current
b) Power = Voltage^2 / Resistance
c) Power = Current^2 * Resistance
d) Power = Voltage * Current * Power Factor
In an AC circuit, the power factor can be improved by:
a) Adding a resistor in series with the load
b) Adding a capacitor in parallel with the load
c) Adding an inductor in parallel with the load
d) All of the above
What is the unit of apparent power in an AC circuit?
a) Watt
b) Volt
c) Ampere
d) Volt-ampere
What is the relationship between real power, apparent power, and power factor in an AC circuit?
a) Real power = Apparent power * Power factor
b) Apparent power = Real power * Power factor
c) Power factor = Real power / Apparent power
d) Power factor = Apparent power / Real power
In an AC circuit, the reactance of an inductor is given by:
a) XL = 2πfL
b) XL = 1 / (2πfL)
c) XL = √(2πfL)
d) XL = 1 / √(2πfL)
In an AC circuit, the reactance of a capacitor is given by:
a) XC = 2πfC
b) XC = 1 / (2πfC)
c) XC = √(2πfC)
d) XC = 1 / √(2πfC)
What is the formula for calculating the impedance in an AC circuit?
a) Impedance = Resistance + Inductive reactance
b) Impedance = Resistance + Capacitive reactance
c) Impedance = √(Resistance^2 + Inductive reactance^2)
d) Impedance = √(Resistance^2 + Capacitive reactance^2)
In an AC circuit, the phase angle between voltage and current can be calculated using the formula:
a) Phase angle = arctan(Inductive reactance / Resistance)
b) Phase angle = arctan(Capacitive reactance / Resistance)
c) Phase angle = arctan(Inductive reactance / Capacitive reactance)
d) Phase angle = arctan(Capacitive reactance / Inductive reactance)
What is the formula for calculating the resonant frequency in an LC circuit?
a) Resonant frequency = 1 / (2π√(LC))
b) Resonant frequency = 1 / (2π√(LC))
c) Resonant frequency = 1 / (2π√(LC))
d) Resonant frequency = 1 / (2π√(LC))
In an AC circuit, the quality factor (Q-factor) of a resonant circuit is a measure of:
a) The sharpness of the resonance
b) The bandwidth of the circuit
c) The power dissipation in the circuit
d) All of the above
What is the formula for calculating the reactance of an inductor at resonance in an LC circuit?
a) XL = 2πfL
b) XL = 0
c) XL = ∞
d) XL = -2πfL
What is the formula for calculating the reactance of a capacitor at resonance in an LC circuit?
a) XC = 2πfC
b) XC = 0
c) XC = ∞
d) XC = -2πfC
What is the formula for calculating the power factor in a series RLC circuit?
a) Power factor = Resistance / Impedance
b) Power factor = Impedance / Resistance
c) Power factor = Resistance / Reactance
d) Power factor = Reactance / Resistance
What is the formula for calculating the power factor in a parallel RLC circuit?
a) Power factor = Impedance / Resistance
b) Power factor = Resistance / Impedance
c) Power factor = Reactance / Resistance
d) Power factor = Resistance / Reactance
What is the formula for calculating the resonant frequency in an RLC circuit?
a) Resonant frequency = 1 / (2π√(LC))
b) Resonant frequency = 1 / (2π√(LC))
c) Resonant frequency = 1 / (2π√(LC))
d) Resonant frequency = 1 / (2π√(LC))
In an RLC circuit, the bandwidth is defined as:
a) The difference between the upper and lower cut-off frequencies
b) The difference between the resonant frequency and the cut-off frequency
c) The difference between the maximum and minimum frequencies
d) The difference between the resonant frequency and the bandwidth frequency
In an AC circuit, the reactance of a resistor is:
a) Zero
b) Non-zero
c) It depends on the frequency
d) It depends on the voltage
In an AC circuit, the reactance of an inductor is:
a) Zero
b) Non-zero
c) It depends on the frequency
d) It depends on the voltage
In an AC circuit, the reactance of a capacitor is:
a) Zero
b) Non-zero
c) It depends on the frequency
d) It depends on the voltage
The time required for an AC circuit to complete one full cycle is called:
a) Frequency
b) Period
c) Wavelength
d) Amplitude
What is the formula for calculating the period of an AC wave?
a) Period = 1 / Frequency
b) Period = Frequency / 2π
c) Period = 2π / Frequency
d) Period = Frequency * 2π
In an AC circuit, the power is transferred from the source to the load during the:
a) Positive half-cycle of the waveform
b) Negative half-cycle of the waveform
c) Entire waveform
d) No power is transferred in an AC circuit
The ratio of the power in an AC circuit to the product of RMS voltage and RMS current is called:
a) Resistance
b) Impedance
c) Power factor
d) Admittance
What is the relationship between frequency and wavelength in an AC wave?
a) Frequency = Wavelength / Speed of light
b) Frequency = Speed of light / Wavelength
c) Frequency = Wavelength * Speed of light
d) Frequency = Speed of light * Wavelength
In an AC circuit, the reactance of a component is directly proportional to:
a) Resistance
b) Frequency
c) Inductance
d) Capacitance
What is the formula for calculating the capacitive reactance in an AC circuit?
a) XC = 1 / (2πfC)
b) XC = 2πfC
c) XC = √(2πfC)
d) XC = 1 / √(2πfC)
What is the formula for calculating the inductive reactance in an AC circuit?
a) XL = 2πfL
b) XL = 1 / (2πfL)
c) XL = √(2πfL)
d) XL = 1 / √(2πfL)
What is the formula for calculating the impedance in an AC circuit with resistance and reactance?
a) Impedance = √(Resistance^2 + Reactance^2)
b) Impedance = Resistance + Reactance
c) Impedance = Resistance – Reactance
d) Impedance = Resistance * Reactance
What is the formula for calculating the phase angle in an AC circuit with resistance and reactance?
a) Phase angle = arctan(Reactance / Resistance)
b) Phase angle = arctan(Resistance / Reactance)
c) Phase angle = arctan(Reactance * Resistance)
d) Phase angle = arctan(Resistance * Reactance)
In an AC circuit, the power is maximum when the phase angle between voltage and current is:
a) 0 degrees
b) 45 degrees
c) 90 degrees
d) 180 degrees
In an AC circuit, the power is minimum when the phase angle between voltage and current is:
a) 0 degrees
b) 45 degrees
c) 90 degrees
d) 180 degrees
What is the relationship between resistance, reactance, and impedance in an AC circuit?
a) Impedance = √(Resistance^2 + Reactance^2)
b) Impedance = Resistance + Reactance
c) Impedance = Resistance – Reactance
d) Impedance = Resistance * Reactance
In an AC circuit, the power dissipated by a resistor can be calculated using the formula:
a) Power = Voltage * Current
b) Power = Voltage^2 / Resistance
c) Power = Current^2 * Resistance
d) Power = Voltage * Current * Power Factor
In an AC circuit, the power dissipated by an inductor or capacitor is:
a) Zero
b) Non-zero
c) It depends on the frequency
d) It depends on the voltage
In an AC circuit, the power is measured in units of:
a) Watts
b) Volts
c) Amperes
d) Volt-amperes
In an AC circuit, the reactive power is measured in units of:
a) Watts
b) Volts
c) Amperes
d) Volt-amperes
In an AC circuit, the power factor can be improved by:
a) Adding a resistor in series with the load
b) Adding a capacitor in parallel with the load
c) Adding an inductor in parallel with the load
d) All of the above
In an AC circuit, the apparent power is equal to:
a) Real power / Power factor
b) Real power * Power factor
c) Real power / Voltage
d) Real power * Voltage
In an AC circuit, the power factor is calculated as the ratio of:
a) Real power to apparent power
b) Apparent power to real power
c) Real power to reactive power
d) Reactive power to real power
What is the formula for calculating the apparent power in an AC circuit?
a) Apparent power = Voltage * Current
b) Apparent power = Voltage^2 / Resistance
c) Apparent power = Current^2 * Resistance
d) Apparent power = Real power / Power factor
In an AC circuit, the power factor can be calculated as the cosine of the:
a) Phase angle
b) Frequency
c) Resistance
d) Reactance
In an AC circuit, the power factor can be improved by:
a) Adding a resistor in series with the load
b) Adding a capacitor in parallel with the load
c) Adding an inductor in parallel with the load
d) All of the above
In an AC circuit, the impedance of a purely resistive load is:
a) Zero
b) Non-zero
c) It depends on the frequency
d) It depends on the voltage
In an AC circuit, the impedance of a purely inductive load is:
a) Zero
b) Non-zero
c) It depends on the frequency
d) It depends on the voltage
In an AC circuit, the impedance of a purely capacitive load is:
a) Zero
b) Non-zero
c) It depends on the frequency
d) It depends on the voltage
In an AC circuit, the impedance of a series RLC circuit is minimum at:
a) Resonance
b) Cut-off frequency
c) Half the resonant frequency
d) Twice the resonant frequency
In an AC circuit, the impedance of a parallel RLC circuit is maximum at:
a) Resonance
b) Cut-off frequency
c) Half the resonant frequency
d) Twice the resonant frequency
In an AC circuit, the resonance frequency is determined by:
a) The inductance and capacitance
b) The resistance and capacitance
c) The resistance and inductance
d) The frequency of the source
In an AC circuit, the bandwidth is defined as:
a) The difference between the upper and lower cut-off frequencies
b) The difference between the resonant frequency and the cut-off frequency
c) The difference between the maximum and minimum frequencies
d) The difference between the resonant frequency and the bandwidth frequency
In an AC circuit, the resonant frequency can be calculated using the formula:
a) Resonant frequency = 1 / (2π√(LC))
b) Resonant frequency = 1 / (2π√(LC))
c) Resonant frequency = 1 / (2π√(LC))
d) Resonant frequency = 1 / (2π√(LC))
In an AC circuit, the quality factor (Q-factor) of a resonant circuit is a measure of:
a) The sharpness of the resonance
b) The bandwidth of the circuit
c) The power dissipation in the circuit
d) All of the above
In an AC circuit, the power factor can be calculated as the cosine of the:
a) Phase angle
b) Frequency
c) Resistance
d) Reactance
In an AC circuit, the power factor can be improved by:
a) Adding a resistor in series with the load
b) Adding a capacitor in parallel with the load
c) Adding an inductor in parallel with the load
d) All of the above
In an AC circuit, the apparent power is equal to:
a) Real power / Power factor
b) Real power * Power factor
c) Real power / Voltage
d) Real power * Voltage
In an AC circuit, the power factor is calculated as the ratio of:
a) Real power to apparent power
b) Apparent power to real power
c) Real power to reactive power
d) Reactive power to real power
What is the formula for calculating the apparent power in an AC circuit?
a) Apparent power = Voltage * Current
b) Apparent power = Voltage^2 / Resistance
c) Apparent power = Current^2 * Resistance
d) Apparent power = Real power / Power factor
In an AC circuit, the power factor can be calculated as the cosine of the:
a) Phase angle
b) Frequency
c) Resistance
d) Reactance
In an AC circuit, the power factor can be improved by:
a) Adding a resistor in series with the load
b) Adding a capacitor in parallel with the load
c) Adding an inductor in parallel with the load
d) All of the above
In an AC circuit, the impedance of a purely resistive load is:
a) Zero
b) Non-zero
c) It depends on the frequency
d) It depends on the voltage