Alternating Current: Class 12 Previous Year Questions

Alternating Current questions asked in CBSE board exams

Repeated questions first. Open the free app to see each question as it appeared in the paper, with its marking scheme.

1.  33. (a) 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 of the circuit and phase difference between V and I. 5 (b) Under what conditions the (i) impedance of the circuit is min…
   Board 20265 markscase-based
2. Assertion (A) : In an ideal step-down transformer, the electrical energy is not lost. Reason (R) : In a step-down transformer, voltage decreases but the current increases. Page 9 of 24 - 17. (a) (b) (ii) ia1 2V. 2R 19. B8.0c 20. 3.0 10-19 400 m 1 210.7 1000 22…
   Board 20251 markAssertion-Reason
3. In the figure X is a coil wound over a hollow wooden pipe. A permanent magnet is pushed at a constant speed v from the right into the pipe and it comes out at the left end of the pipe. During the entry and the exit of the magnet, the current in the wire YZ wil…
   Board 20251 markMCQ
4. A transformer is connected to a 2oo V ac source. The transformer supplies 3000 V to a device. If the number of turns in the primary coil is 450, then the number of turns in its secondary coil is - (A)30 (B)450 (C)4500 (D) 6750
   Board 20251 markMCQ
5. A resistor and an ideal inductor are connected in series to a 2 100 V, 50 Hz ac source. When a voltmeter is connected across the resistor or the inductor, it shows the same reading. The reading of the voltmeter is : (A) 2 100 V (B) 100 V (C) 2 50 V (D) 50 V
   Board 20241 markMCQ
6. A series CR circuit with R = 200 Q and C = (50/·) ·F is connected across an ac source of peak voltage &, = 100 V and frequency v = 50 Hz. Calculate (a) impedance of the circuit (Z), (b) phase angle (p), and (c) voltage across the resistor. Page 13 of 24 30. (a…
   Board 20233 marksshort answer
7. Two metallic spheres of radii a and b respectively are charged and joined by a wire. The ratio of the electric field intensities at the surfaces of the spheres is (a) a/b (b) b/a (c) a2/b2 (d) b2/a2
   CBSE practice 2023-241 markMCQ
8. An inductor of inductance 'L' is connected to an AC source, V = 100 sin ωt. The graph below represents the variation of inductive reactance (XL) of the inductor with the frequency of an alternating source. (a) What is the self-inductance of the inductor? (b) I…
   CBSE practice 2023-245 markscase-based
9. (a) A voltage e = e0 sin t applied to a series LCR circuit drives a current i = i0 sin (t + ) in the circuit. Deduce the expression for the average power dissipated in the circuit. (b) For circuits used for transporting electric power, a low power factor im…
   CBSE practice 2023-245 markscase-based
10. Read the following paragraph and answer the questions that follow. 4 For most mobile devices, the voltage to recharge the battery is typically 5 volts of direct current. In India, the current supplied to our homes is alternating current at 220V and at a freque…
    CBSE practice 2023-244 markscase-based
11. A bulb is connected through a capacitor in an ac circuit as in the circuit (i). The bulb in the circuit glows when the frequency of the input ac voltage is ω. Circuit (i) A circuit (ii) is constructed by including an inductor L as shown, keeping all other comp…
    CBSE practice 2022-233 marksshort answer
12. A pure resistor is connected to an AC power source as shown below. Which of the following statement(s) is/are TRUE? I: The average current flowing through the circuit during one full cycle is zero. 1 II: The current in the resistor leads the voltage by π/2. II…
    CBSE practice 2023-241 markMCQ

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