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Class 12 Physics: Alternating Current
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MCQs on ac generator, ac voltage applied to resistor, inductor and capacitor, phasors, ac circuit power, lc oscillations, transformers and displacement current.
 

Class 12 Physics: Alternating Current
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25 Questions

1. Which among the following is the correct expression for finding capacitive reactance for an ac circuit containing capacitor only?
2. Which among the following is true about transformers?
3. Determine the peak current if an inductor of inductance 500 mH is connected to an ac source of peak emf 650 V and frequency 100 Hz
4. Adithya peddles a stationary bicycle the pedals of which are attached to a 500 turn coil of area 11 m2. The coil rotates at half a revolution per second and it is placed in a uniform magnetic field of 20.5 T perpendicular to the axis of rotation of the coil. What is the maximum voltage generated in the coil?
5. Which one of the following current flows in the gap between the capacitor plates?
6. A series circuit with L = 0.12 H, C = 0.48 mF and R = 25 Ω is connected to a 220 V variable frequency power supply. At what frequency is the circuit current maximum?
7. What is the most common application of LC oscillators?
8. Find out the rms value of current in the circuit wherein a 35 mH inductor is connected to 200 V, 70 Hz ac supply.
9. What is the general expression of a sinusoidal signal?
10. A 1.50 μF capacitor is connected to a 220 V, 50 Hz source. If the frequency is doubled, what happens to the capacitive reactance?
11. When are the voltage and current in LCR-series ac circuit in phase?
12. How will the capacitive reactance be affected if the frequency is doubled?
13. What does a phasor represent?
14. Why does an inductor offer an easy path to dc and a resistive path to ac?
15. A resistor of 50 Ω, an inductor of \(\frac {20}{\pi}\) H and a capacitor of \(\frac {5}{\pi }\) μF are connected in series to a voltage supply of 230 V – 50 Hz. Find the impedance of the circuit.
16. Determine the rms value of current in the circuit if a 50 Ω resistor is connected across an ac source of 200 V, 50 Hz?
17. In a step-down transformer, the number of turns in the secondary coil is 20 and the number of turns in the primary coil is 100. If the voltage applied to the primary coil is 120 V, then what is the voltage output from the secondary coil?
18. What will be the rms value of the voltage, if the sinusoidal value voltage is given as E = 100 sin 314 t applied across a resistor of resistance 15 ohms?
19. 'X' is a rectangular coil consisting of a large number of turns of copper wire wound over a soft iron core in an a.c. generator. Identify X.
20. Which value of the current do you measure with an a.c. ammeter?
21. Which among the following varies in both magnitude and sign over a cycle?
22. A parallel plate capacitor with plate area A and separation between the plates d, is charged by a constant current I. Consider a plane surface of area A/4 parallel to the plates and drawn between the plates. What is the displacement current through this area?
23. An a.c. generator consists of a coil of 1000 turns and cross-sectional area of 3m2, rotating at a constant angular speed of 60 rad s-1 in a uniform magnetic field 0.04 T. The resistance of the coil is 500Ω. Calculate the maximum current drawn from the generator.
24. Identify the function of a phasor from the following.
25. Identify the principle behind the working of an a.c. generator.

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