Alternating Current

CBSE Class 12 Physics · every board question from this chapter, 2023–2026 · 24 of them repeated across years

• Which of the following statements is not true for electric energy in ac form compared to that in dc form?2026asked 3×
• An ac voltage is given as v=14 sin (314 t) V. The average and the effective value of the voltage (in V ) over a cycle are…2026asked 3×
• In a series LCR circuit, the voltage across the resistor, capacitor and inductor is 10 V each. If the capacitor is short…2026
• The figure shows the variation of capacitive reactance (X C) of two ideal capacitors of capacitances C 1 \& C 2 with the…2026asked 3×
• A resistor and an inductor of negligible resistance are connected in series to a 20 V ac source. If the voltage across the…2026
• A series LCR circuit with R=3 Ω, X C=4 Ω, X L=8 Ω is connected to a 220 V, 50 Hz ac source. The power factor for the circuit is2026
• The rms and the average value of an ac voltage V=V 0 sin ω t volt over a cycle respectively will be:2026asked 3×
• Differentiate between inductive reactance, capacitive reactance and impedance of an ac circuit. An ideal inductor and an ideal…2026
• Can a transformer step up or step down dc power supply? Can a step up transformer work as a step down transformer? Does a step up…2026
• Discuss the behaviour of an inductor connected to (i) a dc source, and (ii) a high frequency ac source. What is the phase…2026
• A series combination of circuit elements X and Y is connected across an ac source. It is found that the voltage is ahead of…2026
• (i) A light bulb and an open coil inductor are connected in series across an ac source of variable frequency. How will the glow…2026asked 3×
• (i) Define the terms (I) resonant frequency, and (II) power factor of a series LCR circuit. For what value of the power factor…2026asked 3×
• A series combination of L, C and R is connected to an a.c. source. Using a phasor diagram, derive an expression for the impedance…2026asked 3×
• A capacitor of capacitance C has reactance X in an ac circuit. If the capacitance and the frequency of the applied voltage are…2025
• An alternating current is given by I=I 0 cos (100 π) t. The least time the current takes to decrease from its maximum value to…2025asked 3×
• The ratio of the number of turns of the primary to the secondary coils in an ideal transformer is 20: 1. If 240 V ac is applied…2025
• A capacitor and an inductor are connected in series across an ac source of voltage of variable frequency. The frequency is…2025asked 3×
• A transformer is a device used for converting:2025
• A voltage ν=ν 0 sin ω t applied to a circuit drives a current i=i 0 sin (ω t+φ) in the circuit. The average power consumed in the…2025asked 3×
• An ammeter connected in series in an ac circuit reads 10 A. The maximum value of current at any instant in the circuit is:2025
• A transformer is connected to a 200 V ac source. The transformer supplies 3000 V to a device. If the number of turns in the…2025
• The number of turns between different pairs of output terminals are shown for a step-up transformer. Input voltage of 20 V is…2025
• An ac source is connected to a resistor and an inductor in series. The voltage across the resistor and inductor are 8 V and 6 V…2025asked 3×
• The alternating current I in an inductor is observed to vary with time t as shown in the graph for a cycle. Which one of the…2025asked 3×
• Assertion: A series LCR circuit behaves as a pure resistive circuit at resonance. Reason (R): At resonance, X L=X C gives ω= 1√LC.2025asked 3×
• Assertion: In an ideal step-down transformer, the electrical energy is not lost. Reason (R): In a step-down transformer, voltage…2025asked 3×
• An ac source of voltage ν=ν m sin ω t is connected to a series combination of LCR circuit. Draw the phasor diagram. Using it…2025
• ac voltage of frequency ω is applied across a series LCR circuit. Draw the phasor diagram and obtain the impedance of the…2025
• Differentiate between the peak value and root mean square value of an alternating current. Derive the expression for the root…2025
• An ac source of voltage V=V 0 sin ω t is connected to a circuit element X. It is observed that the current flowing through X…2025
• (i) Write the principle of working of an ac generator. Draw its labelled diagram and explain its working. (ii) A resistor of 400…2025asked 3×
• An ac voltage is applied across an ideal inductor. The current in it2024
• A resistor and an ideal inductor are connected in series to a 100 √2 V, 50 Hz ac source. When a voltmeter is connected across the…2024
• In an ac circuit, the instantaneous values of current (in A) and voltage (in V ) are I=5 sin ω t and E=200 cos (ω t+(π)/3)…2024
• A series LCR circuit ( L=2 mH, C=0 · 2 μ F and R=30 Ω ) is connected to an ac source of variable frequency. The impedance of this…2024
• The average value of the alternating voltage v=(157 V) sin ω t over its first half-cycle is:2024
• The reactance of a capacitor of capacitance C connected to an ac source of frequency ω is ' X '. If the capacitance of the…2024
• The primary and secondary coils of a transformer have 500 turns and 5000 turns respectively. The primary coil is connected to an…2024
• Figure shows the variation of inductive reactance X L of two ideal inductors of inductance L 1 and L 2, with angular frequency ω.…2024
• The r.m.s. value of a current given by i=(i 1 cos ω t+i 2 sin ω t) is -2024
• An ac source V=282 sin (100 t) volt is connected across a 1 μ F capacitor. The rms value of current in the circuit will be (take…2024
• Distinguish between reactance and impedance of an ac circuit. Show that an ideal inductor in an ac circuit does not dissipate any…2024
• A sinusoidal voltage is applied to an electric circuit containing a circuit element ' X ' in which the current leads the voltage…2024
• An ac voltage v i=140 sin (100 π t) V is applied to the primary coil having 200 turns, of an ideal transformer and it supplies a…2024
• Draw the graphs showing the variation of the following with the frequency of ac source in a circuit: (i) Resistance (ii)…2024
• An inductor, a capacitor and a resistor are connected in series with an ac source v=v m sin ω t. Derive an expression for the…2024
• (i) A resistor and a capacitor are connected in series to an ac source v=v m sin ω t. Derive an expression for the impedance of…2024asked 3×
• (i) You are given three circuit elements X, Y and Z. They are connected one by one across a given ac source. It is found that V…2024asked 3×
• (i) Mention the factors on which the resonant frequency of a series LCR circuit depends. Plot a graph showing variation of…2024asked 3×
• The figure shows variation of current (I) with time ( t ) in four devices P, Q, R and S. The device in which an alternating…2023asked 3×
• An inductor, a capacitor and a resistor are connected in series across an ac source of voltage. If the frequency of the source is…2023asked 3×
• An ac voltage v=v 0 sin ω t is applied to a series combination of a resistor R and an element X. The instantaneous current in the…2023asked 3×
• Which of the following statements about a series LCR circuit connected to an ac source is correct?2023
• An ideal inductor is connected across an AC source of voltage. The current in the circuit2023
• What is the ratio of inductive and capacitive reactance in an ac circuit?2023
• A voltage signal is described by: for a cycle. Its rms value is:2023
• A series RL circuit with R=10 Ω and L=(100/(π)) mH is connected to an ac source of voltage V=141 sin (100 π t), where V is in…2023
• An ac voltage v=v m sin ω t(v m=310 V. and.f=50 Hz) is connected to a pure capacitor of capacitance 15 μ F. Calculate (i) the…2023
• An alternating current I=14 sin (100 π t) A passes through a series combination of a resistor of 30 Ω and an inductor of (2/(5…2023
• How does the resistance differ from impedance? With the help of a suitable phasor diagram, obtain an expression for impedance of…2023asked 3×
• A current of 1 A flows through a coil when it is connected across a DC battery of 100 V. If DC battery is replaced by an AC…2023
• An alternating voltage of 220 V is applied across a device X. A current of 0.22 A flows in the circuit and it lags behind the…2023
• A resistor of 30 Ω and a capacitor of 250/(π) μ F are connected in series to a 200 V, 50 Hz ac source. Calculate (i) the current…2023asked 3×
• The primary coil having N p turns of an ideal transformer is supplied with an alternating voltage V p. Obtain an expression for…2023
• A series CR circuit with R=200 Ω and C=(50 / π) μ F is connected across an ac source of peak voltage ε 0=100 V and frequency v=50…2023
• An ac source v=v m sin ω t is connected across an ideal capacitor. Derive the expression for the (i) current flowing in the…2023asked 3×
• The primary and the secondary coils of an ideal step-down transformer consist of 650 and 25 turns respectively. When the primary…2023
• A resistor of 50 Ω, a capacitor of (25/(π)) μ F and an inductor of (4/(π)) H are connected in series across an ac source whose…2023

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