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AC Circuits

89 Questions Start DPT Test
All Exams DPT (89)
Q1 DPT MCQ
26 Aug 2026
Concept:
If the frequency of an alternating current is 50 Hz then the time taken for the change from zero to positive peak value and positive peak value to negative peak value of current are respectively
A.
1/200 sec, 1/100 sec
B.
1/100 sec, 1/200 sec
C.
200 sec, 100 sec
D.
1/50 sec, 1/100 sec
Q2 DPT MCQ
26 Aug 2026
Concept:
What will be the equation of ac of frequency 75 Hz if its r.m.s. value is 20 A
A.
$i = 20 \sin 150 \pi t$
B.
$i = 20\sqrt{2} \sin(150 \pi t)$
C.
$i = \frac{20}{\sqrt{2}} \sin(150 \pi t)$
D.
$i = 20\sqrt{2} \sin(75\pi t)$
Q3 DPT MCQ
26 Aug 2026
Concept:
At what time (From zero) the alternating voltage becomes $\frac{1}{\sqrt{2}}$ times of it's peak value. Where T is the periodic time
A.
$\frac{T}{2}$ sec
B.
$\frac{T}{4}$ sec
C.
$\frac{T}{8}$ sec
D.
$\frac{T}{12}$ sec
Q4 DPT MCQ
26 Aug 2026
Concept:
The peak value of an alternating e.m.f. E is given by $E = E_{0} \cos \omega t$ is 10 volts and its frequency is 50 Hz. At time $t = \frac{1}{600}$ sec, the instantaneous e.m.f. is
A.
10 V
B.
$5\sqrt{3}$ V
C.
5 V
D.
1 V
Q5 DPT MCQ
26 Aug 2026
Concept:
The instantaneous value of current in an ac circuit is $i = 2 \sin (100\pi t + \pi/3)$ A. The current at the beginning ($t = 0$) will be
A.
$2\sqrt{3}$ A
B.
$\sqrt{3}$ A
C.
$\frac{\sqrt{3}}{2}$ A
D.
Zero
Q6 DPT MCQ
26 Aug 2026
Concept:
The voltage of an ac source varies with time according to the equation $V = 100 \sin(100\pi t) \cos(100\pi t)$ where $t$ is in seconds and $V$ is in volts. Then
A.
The peak voltage of the source is 100 volts
B.
The peak voltage of the source is 50 volts
C.
The peak voltage of the source is $100/\sqrt{2}$ volts
D.
The frequency of the source is 50 Hz
Q7 DPT MCQ
26 Aug 2026
Concept:
If the frequency of ac is 60 Hz the time difference corresponding to a phase difference of $60^{\circ}$ is
A.
60 sec
B.
1 sec
C.
$\frac{1}{60}$ sec
D.
$\frac{1}{360}$ sec
Q8 DPT MCQ
26 Aug 2026
Concept:
In an ac circuit, V and i are given by $V = 100 \sin(100 t)$ volt, and $i = 100 \sin(100 t + \frac{\pi}{3})$ mA. The power dissipated in circuit is
A.
$10^{4}$ watt
B.
10 watt
C.
2.5 watt
D.
5 watt
Q9 DPT MCQ
26 Aug 2026
Concept:
In a circuit an alternating current and a direct current are supplied together. The expression of the instantaneous current is given as $i = 3 + 6 \sin \omega t$. Then the r.m.s. value of the current is
A.
3 A
B.
6 A
C.
$3\sqrt{2}$ A
D.
$3\sqrt{3}$ A
Q10 DPT MCQ
26 Aug 2026
Concept:
The r.m.s. value of the alternating e.m.f. $E = (8 \sin \omega t + 6 \sin 2\omega t)$ V is
A.
7.05 V
B.
14.14 V
C.
10 V
D.
20 V
Q11 DPT MCQ
26 Aug 2026
Concept:
Voltage and current in an ac circuit are given by $V = 5 \sin(100\pi t - \frac{\pi}{6})$ and $i = 4 \sin(100\pi t + \frac{\pi}{6})$
A.
Voltage leads the current by $30^{\circ}$
B.
Current leads the voltage by $30^{\circ}$
C.
Current leads the voltage by $60^{\circ}$
D.
Voltage leads the current by $60^{\circ}$
Q12 DPT MCQ
26 Aug 2026
Concept:
The instantaneous values of current and potential difference in an alternating circuit are $i = \sin \omega t$ and $E = 100 \cos \omega t$ respectively. r.m.s. value of wattless current (in amp) in the circuit is
A.
1
B.
$\frac{1}{\sqrt{2}}$
C.
100
D.
Zero
Q13 DPT MCQ
26 Aug 2026
Concept:
The r.m.s. current in an ac circuit is 2 A. If the wattless current be $\sqrt{3} A$, what is the power factor
A.
$\frac{1}{\sqrt{3}}$
B.
$\frac{1}{\sqrt{2}}$
C.
$\frac{1}{2}$
D.
$\frac{1}{3}$
Q14 DPT MCQ
26 Aug 2026
Concept:
The r.m.s. value of alternating current in a circuit is 4 A and power factor is 0.5. If the power dissipated in the circuit is 100W, then the peak value of voltage in the circuit is
A.
50 volt
B.
100 volt
C.
35 volt
D.
70 volt
Q15 DPT MCQ
26 Aug 2026
Concept:
the impedance of an ac circuit is $200~\Omega$ and the phase angle between current and e.m.f is $60^{\circ}$. What is the resistance of the circuit
A.
$50~\Omega$
B.
$300~\Omega$
C.
$100~\Omega$
D.
$100\sqrt{3}~\Omega$
Q16 DPT MCQ
26 Aug 2026
Concept:
An ac voltage source of $E = 150~sin~100~t$ is used to run a device which offers a resistance of $20~\Omega$ and restricts the flow of current in one direction only. The r.m.s. value of current in the circuit will be
A.
1.58 A
B.
0.98 A
C.
3.75 A
D.
2.38 A
Q17 DPT MCQ
26 Aug 2026
Concept:
From the image given below, two sinusoidal voltages of the same frequency are shown in the diagram. What is the frequency, and the phase relationship between the voltages image.png
A.
$0.4~Hz, -\frac{\pi}{4}$
B.
$2.5~Hz, +\frac{\pi}{2}$
C.
$2.5~Hz, -\frac{\pi}{2}$
D.
$2.5~Hz, -\frac{\pi}{4}$
Q18 DPT MCQ
26 Aug 2026
Concept:
In a resistive circuit $R = 10~\Omega$ and applied alternating voltage $V = 100~sin~100~\pi~t$, find the peak current, r.m.s. current, average current, and frequency respectively
A.
$10~A,~5\sqrt{2}~A,~6.37~A,~50~Hz$
B.
$5~A,~10~A,~3.14~A,~100~Hz$
C.
$10\sqrt{2}~A,~5~A,~5~A,~50~Hz$
D.
$10~A,~10~A,~6.37~A,~25~Hz$
Q19 DPT MCQ
26 Aug 2026
Concept:
In a resistive circuit $R = 10~\Omega$ and applied alternating voltage $V = 100~sin~100~\pi~t$, find the time period, power factor, power dissipated, and time difference respectively
A.
$0.02~sec,~1,~500~W,~0$
B.
$0.05~sec,~0,~250~W,~T/2$
C.
$0.02~sec,~0,~0~W,~T/4$
D.
$0.01~sec,~1,~500~W,~T/2$
Q20 DPT MCQ
26 Aug 2026
Concept:
In a purely inductive circuit if $L = \frac{100}{\pi} \times 10^{-3}~H$ and applied alternating voltage is given by $V = 100~sin~100~\pi~t$, find the frequency and time period respectively
A.
$50~Hz,~0.02~sec$
B.
$100~Hz,~0.01~sec$
C.
$25~Hz,~0.04~sec$
D.
$50~Hz,~0.05~sec$
Q21 DPT MCQ
26 Aug 2026
Concept:
An alternating voltage $E = 200\sqrt{2}~sin(100~t)$ is connected to a 1 microfaracd capacitor through an ac ammeter. The reading of the ammeter shall be
A.
10 mA
B.
40 mA
C.
80 mA
D.
20 mA
Q22 DPT MCQ
26 Aug 2026
Concept:
The current and voltage in an ac circuit are respectively given by i = sin 314 t and e = 200 sin (314 t + pi / 3) from the image given below. If the resistance is $100$ ohm, then the reactance of the circuit is
A.
$100 / \sqrt{3}$ ohm
B.
$200$ ohm
C.
$100 \sqrt{3}$ ohm
D.
$200 \sqrt{3}$ ohm
Q23 DPT MCQ
26 Aug 2026
Concept:
A bulb of $60$ volt and $10$ watt is connected with $100$ volt of ac source with an inductance coil in series. If bulb illuminates with it's full intensity then value of inductance of coil is from the image given below
A.
$1.28$ H
B.
$2.15$ H
C.
$3.27$ H
D.
$3.89$ H
Q24 DPT MCQ
26 Aug 2026
Concept:
When $100$ volt dc is applied across a solenoid, a current of $1.0$ amp flows in it. When $100$ volt ac is applied across the same coil, the current drops to $0.5$ amp. If the frequency of ac source is $50$ Hz the impedance and inductance of the solenoid are from the image gven below
A.
$200$ ohms and $0.5$ henry
B.
$100$ ohms and $0.86$ henry
C.
$200$ ohms and $1.0$ henry
D.
$100$ ohms and $0.93$ henry
Q25 DPT MCQ
26 Aug 2026
Concept:
In an ac circuit, containing an inductance and a capacitor in series, the current is found to be maximum when the value of inductance is $0.5$ henry and a capacitance of $8 \ \mu F$. The angular frequency of the input ac voltage must be equal to from the image gven below
A.
$500$ rad/sec
B.
$5 \times 10^{4}$ rad/sec
C.
$4000$ rad/sec
D.
$5000$ rad/sec
Q26 DPT MCQ
26 Aug 2026
Concept:
A resistance of $40$ ohm and an inductance of $95.5$ millihenry are connected in series in a $50$ cycles/second ac circuit. The impedance of this combination is very nearly from the image gven below
A.
$30$ ohm
B.
$400$ ohm
C.
$50$ ohm
D.
$60$ ohm
Q27 DPT MCQ
26 Aug 2026
Concept:
A $\frac{2.5}{\pi} \ \mu F$ capacitor and $3000$-ohm resistance are joined in series to an ac source of $200$ volt and $50 \text{ sec}^{-1}$ frequency. The power factor of the circuit and the power dissipated in it will respectively be from the image gven below
A.
$0.6, 0.06 \text{ W}$
B.
$0.06, 0.6 \text{ W}$
C.
$0.6, 4.8 \text{ W}$
D.
$4.8, 0.6 \text{ W}$
Q28 DPT MCQ
26 Aug 2026
Concept:
A telephone wire of length $200 \ km$ has a capacitance of $0.014 \ \mu F$ per $km$. If it carries an ac of frequency $5 \ kHz$, what should be the value of an inductor required to be connected in series so that the impedance of the circuit is minimum from the image gven below
A.
$0.35 \ mH$
B.
$35 \ mH$
C.
$3.5 \ mH$
D.
Zero
Q29 DPT MCQ
26 Aug 2026
Concept:
A resistance of $40$ ohm and an inductance of $95.5$ millihenry are connected in series in a $50$ cycles/second ac circuit. The impedance of this combination is very nearly
A.
$30$ ohm
B.
$60$ ohm
C.
$40$ ohm
D.
$50$ ohm
Q30 DPT MCQ
26 Aug 2026
Concept:
In an ac circuit, containing an inductance and a capacitor in series, the current is found to be maximum when the value of inductance is $0.5$ henry and a capacitance of $8 \ \mu F$. The angular frequency of the input ac voltage must be equal to from the image gven below
A.
$500$ rad/sec
B.
$5 \times 10^{4}$ rad/sec
C.
$4000$ rad/sec
D.
$5000$ rad/sec
Q31 DPT AC Currents MCQ
29 Aug 2026
Concept:
A telephone wire of length 200 km has a capacitance of 0.014 microfarad per km. If it carries an ac of frequency 5 kHz, what should be the value of an inductor required to be connected in series so that the impedance of the circuit is minimum
A.
3.5 mH
B.
0.35 mH
C.
35 mH
D.
Zero
Q32 DPT AC Currents MCQ
29 Aug 2026
Concept:
A $\frac{2.5}{\pi} \ \mu F$ capacitor and $3000$-ohm resistance are joined in series to an ac source of $200$ volt and $50 \text{ sec}^{-1}$ frequency. The power factor of the circuit and the power dissipated in it will respectively be from the image gven below
A.
$0.6, 0.06 \text{ W}$
B.
$0.06, 0.6 \text{ W}$
C.
$0.6, 4.8 \text{ W}$
D.
$4.8, 0.6 \text{ W}$
Q33 DPT AC Currents MCQ
29 Aug 2026
Concept:
A telephone wire of length $200 \ km$ has a capacitance of $0.014 \ \mu F$ per $km$. If it carries an ac of frequency $5 \ kHz$, what should be the value of an inductor required to be connected in series so that the impedance of the circuit is minimum from the image gven below
A.
$0.35 \ mH$
B.
$35 \ mH$
C.
$3.5 \ mH$
D.
Zero
Q34 DPT AC Currents MCQ
29 Aug 2026
Concept:
Find out instantaneous current value for $I = I_{0} \sin(\omega t)$ at $t = \frac{T}{8}$
A.
$\frac{I_{0}}{2}$
B.
$\frac{I_{0}}{\sqrt{2}}$
C.
$\sqrt{2} I_{0}$
D.
$I_{0}$
Q35 DPT AC Currents MCQ
29 Aug 2026
Concept:
Find out instantaneous voltage for $V = 200 \sin (400 \pi t)$ at $t = \frac{1}{800}$ sec
A.
$100$ V
B.
$200$ V
C.
$200\sqrt{2}$ V
D.
$100\sqrt{2}$ V
Q36 DPT AC Currents MCQ
29 Aug 2026
Concept:
Find out instantaneous value for $I = I_{0} \sin\left(\omega t - \frac{\pi}{6}\right)$ at $t = \frac{T}{2}$
A.
$\frac{I_{0}}{2}$
B.
$I_{0}$
C.
$\frac{I_{0}}{\sqrt{2}}$
D.
$0$
Q37 DPT AC Currents MCQ
29 Aug 2026
Concept:
Find the time taken by current to reach $\frac{I_{0}}{\sqrt{2}}$ if the frequency of current is $50$ Hz
A.
$1.5$ ms
B.
$2.5$ ms
C.
$5.0$ ms
D.
$10.0$ ms
Q38 DPT AC Currents MCQ
29 Aug 2026
Concept:
If an alternating current main supply is given to be $220$ V. What would be the average e.m.f. during a positive half cycle?
A.
$155$ V
B.
$198$ V
C.
$220$ V
D.
$311$ V
Q39 DPT AC Currents MCQ
29 Aug 2026
Concept:
Find RMS value of $I = 3 + 4 \sin\left(\omega t + \frac{\pi}{3}\right)$
A.
$\sqrt{15}$
B.
$\sqrt{17}$
C.
$\sqrt{19}$
D.
$\sqrt{21}$
Q40 DPT AC Currents MCQ
29 Aug 2026
Concept:
Find out RMS value of following currents (i) $I = a + b \sin(\omega t)$ (ii) $I = a \sin(\omega t) + b \cos(\omega t)$
A.
(i) $\sqrt{a^{2} + \frac{b^{2}}{2}}$, (ii) $\sqrt{\frac{a^{2}}{2} + \frac{b^{2}}{2}}$
B.
(i) $\sqrt{a^{2} + b^{2}}$, (ii) $\sqrt{a^{2} + \frac{b^{2}}{2}}$
C.
(i) $\sqrt{\frac{a^{2}}{2} + b^{2}}$, (ii) $\sqrt{a^{2} + b^{2}}$
D.
(i) $a + \frac{b}{\sqrt{2}}$, (ii) $\frac{a + b}{\sqrt{2}}$
Q41 DPT MCQ
26 Aug 2026
Concept:
The equation of an alternating current is $i = 50\sqrt{2} \sin 400\pi t$ ampere then the frequency and the root mean square of the current are respectively
A.
400 $\pi$ Hz, $50\sqrt{2}$ amp
B.
50 Hz, 200 amp
C.
200 Hz, 50 amp
D.
200 Hz, $50\sqrt{2}$ amp
Q42 DPT MCQ
26 Aug 2026
Concept:
A bulb of $60$ volt and $10$ watt is connected with $100$ volt of ac source with an inductance coil in series. If bulb illuminates with it's full intensity then value of inductance of coil is from the image given below
A.
$1.28$ H
B.
$2.15$ H
C.
$3.27$ H
D.
$3.89$ H
Q43 DPT MCQ
26 Aug 2026
Concept:
When 100 volt dc is applied across a solenoid, a current of 1.0 amp flows in it. When 100 volt ac is applied across the same coil, the current drops to 0.5 amp. If the frequency of ac source is 50 Hz the impedance and inductance of the solenoid are
A.
200 ohms and 0.5 henry
B.
100 ohms and 0.86 henry
C.
200 ohms and 1.0 henry
D.
100 ohms and 0.93 henry
Q44 DPT MCQ
26 Aug 2026
Concept:
In an ac circuit, containing an inductance and a capacitor in series, the current is found to be maximum when the value of inductance is 0.5 henry and a capacitance of 8 micro farad. The angular frequency of the input ac voltage must be equal to
A.
500 rad/sec
B.
$5 \times 10^4$ rad/sec
C.
4000 rad/sec
D.
5000 rad/sec
Q45 DPT MCQ
26 Aug 2026
Concept:
A resistance of $40$ ohm and an inductance of $95.5$ millihenry are connected in series in a $50$ cycles/second ac circuit. The impedance of this combination is very nearly
A.
$30$ ohm
B.
$60$ ohm
C.
$40$ ohm
D.
$50$ ohm
Q46 DPT MCQ
26 Aug 2026
Concept:
In an ac circuit, containing an inductance and a capacitor in series, the current is found to be maximum when the value of inductance is $0.5$ henry and a capacitance of $8 \ \mu F$. The angular frequency of the input ac voltage must be equal to from the image gven below
A.
$500$ rad/sec
B.
$5 \times 10^{4}$ rad/sec
C.
$4000$ rad/sec
D.
$5000$ rad/sec
Q47 DPT MCQ
26 Aug 2026
Concept:
$\frac{2.5}{\pi} \mu F$ capacitor and $3000$-ohm resistance are joined in series to an ac source of $200$ volt and $50 \text{ sec}^{-1}$ frequency. The power factor of the circuit and the power dissipated in it will respectively
A.
$0.6, 0.06 W$
B.
$0.06, 0.6 W$
C.
$0.6, 4.8 W$
D.
$4.8, 0.6 W$
Q48 DPT MCQ
26 Aug 2026
Concept:
A telephone wire of length 200 km has a capacitance of 0.014 microfarad per km. If it carries an ac of frequency 5 kHz, what should be the value of an inductor required to be connected in series so that the impedance of the circuit is minimum
A.
3.5 mH
B.
0.35 mH
C.
35 mH
D.
Zero
Q49 DPT MCQ
26 Aug 2026
Concept:
A $\frac{2.5}{\pi} \ \mu F$ capacitor and $3000$-ohm resistance are joined in series to an ac source of $200$ volt and $50 \text{ sec}^{-1}$ frequency. The power factor of the circuit and the power dissipated in it will respectively be from the image gven below
A.
$0.6, 0.06 \text{ W}$
B.
$0.06, 0.6 \text{ W}$
C.
$0.6, 4.8 \text{ W}$
D.
$4.8, 0.6 \text{ W}$
Q50 DPT AC Currents MCQ
29 Aug 2026
Concept:
The current and voltage in a circuit are given by $i = 3.5 \sin (628 t + 30^{\circ})$ A and $V = 28 \sin (628 t - 30^{\circ})$ volt. Find (a) time period of current (b) phase difference between voltage and current.
A.
$T = 0.02$ s, $\Delta\phi = 30^{\circ}$
B.
$T = 0.01$ s, $\Delta\phi = 60^{\circ}$
C.
$T = 0.01$ s, $\Delta\phi = 30^{\circ}$
D.
$T = 0.02$ s, $\Delta\phi = 60^{\circ}$