Dòng điện xoay chiều Practice Questions
THPT (Vietnam) · THPT Vật lý · 146 free MCQs with instant results and detailed explanations.
146
Total
51
Easy
69
Medium
26
Hard
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Sample Questions from Dòng điện xoay chiều
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Q1
Easy
In an AC circuit, if the frequency of the applied voltage is doubled, what happens to the impedance of a pure inductor?
A.
It doubles
B.
It remains the same
C.
It halves
D.
It quadruples
Show Answer & Explanation
Correct Answer: C
The impedance of a pure inductor is given by Z = 2πfL. If the frequency f is doubled, the impedance Z will halve, since it is directly proportional to frequency.
Q2
Easy
What is the effect of increasing the capacitance in an AC circuit at a constant frequency?
A.
Increases the reactance
B.
Decreases the reactance
C.
Has no effect
D.
Increases the voltage
Show Answer & Explanation
Correct Answer: B
The capacitive reactance is given by Xc = 1/(2πfC). Increasing capacitance (C) decreases the reactance (Xc), which allows more current to flow.
Q3
Easy
In a series AC circuit consisting of resistance and inductance, which parameter is responsible for phase difference between voltage and current?
A.
Resistance
B.
Inductance
C.
Capacitance
D.
Frequency
Show Answer & Explanation
Correct Answer: B
In a series AC circuit, inductance causes a phase shift, where the current lags the voltage. The reactance of the inductor affects this phase difference significantly.
Q4
Medium
In an AC circuit, if the frequency of the source is doubled, what happens to the inductive reactance?
A.
It doubles.
B.
It remains the same.
C.
It is halved.
D.
It quadruples.
Show Answer & Explanation
Correct Answer: C
Inductive reactance (XL) is given by the formula XL = 2πfL. If the frequency (f) is doubled, XL becomes halved since it is inversely proportional to frequency.
Q5
Medium
A capacitor is connected in an AC circuit with a frequency of 50 Hz. If the capacitance is 20 microfarads, what is the capacitive reactance?
A.
159.15 ohms
B.
318.30 ohms
C.
7.96 ohms
D.
31.83 ohms
Show Answer & Explanation
Correct Answer: A
Capacitive reactance (XC) can be calculated using the formula XC = 1/(2πfC). Substituting the values gives XC = 159.15 ohms.
Q6
Medium
Which of the following statements about the impedance in an RLC series circuit is true?
A.
Impedance equals resistance only.
B.
Impedance decreases with increasing frequency.
C.
Impedance is the vector sum of resistance and reactance.
D.
Impedance is always less than resistance.
Show Answer & Explanation
Correct Answer: C
In an RLC series circuit, impedance (Z) is the vector sum of resistance (R) and reactance (X), not just resistance alone.
Q7
Medium
In a series AC circuit with an inductor and a capacitor, what effect does increasing the inductance have on the resonant frequency?
A.
Resonant frequency increases.
B.
Resonant frequency decreases.
C.
Resonant frequency remains unchanged.
D.
Resonant frequency becomes zero.
Show Answer & Explanation
Correct Answer: B
The resonant frequency (f0) is given by the formula f0 = 1/(2π√(LC)). Increasing the inductance (L) decreases the resonant frequency.
Q8
Hard
In an AC circuit, the voltage across a capacitor is given by V = V0 sin(ωt). If the peak voltage V0 is 100V and the frequency is 50Hz, what is the capacitive reactance at a capacitance of 20μF?
A.
159.15 Ω
B.
79.58 Ω
C.
318.31 Ω
D.
39.79 Ω
Show Answer & Explanation
Correct Answer: A
The capacitive reactance (Xc) is calculated using the formula Xc = 1 / (2πfC). Plugging in the values: f = 50 Hz and C = 20 μF (20 x 10^-6 F), we get Xc = 1 / (2π(50)(20 x 10^-6)) = 159.15 Ω. Thus, option A is correct.
Q9
Hard
A series RLC circuit has a resistance of 10Ω, an inductance of 0.1H, and a capacitance of 100μF. What is the resonant frequency of this circuit?
A.
159.15 Hz
B.
100 Hz
C.
79.58 Hz
D.
50 Hz
Show Answer & Explanation
Correct Answer: A
The resonant frequency (fr) of a series RLC circuit is given by fr = 1 / (2π√(LC)). Substituting L = 0.1 H and C = 100 μF (100 x 10^-6 F), we find fr = 1 / (2π√(0.1 * 100 x 10^-6)) = 159.15 Hz. Hence, option A is correct.
Q10
Hard
In an AC circuit with a resistor and inductor in series, the impedance is given by Z = √(R² + (X_L)²), where R is resistance and X_L is inductive reactance. If R = 4 Ω and X_L = 3 Ω, what is the impedance of the circuit?
A.
5 Ω
B.
7 Ω
C.
10 Ω
D.
12 Ω
Show Answer & Explanation
Correct Answer: A
The impedance Z is calculated using the formula Z = √(R² + (X_L)²). Substituting R = 4 Ω and X_L = 3 Ω gives Z = √(4² + 3²) = √(16 + 9) = √25 = 5 Ω.
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Dòng điện xoay chiều — THPT (Vietnam) THPT Vật lý Practice Questions Online
This page contains 146 practice MCQs for the chapter Dòng điện xoay chiều in THPT (Vietnam) THPT Vật lý. The questions are organized by difficulty — 51 easy, 69 medium, 26 hard — so you can choose the right level for your preparation.
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