This quiz works best with JavaScript enabled. Home > Cbse > Class 12 > Science > Physics Part I > Class 12 Physics (Part I) Chapter 7 Alternating Current – Quiz 9 🏠 Homepage 📘 Download PDF Books 📕 Premium PDF Books Class 12 Physics (Part I) Chapter 7 Alternating Current Quiz 9 (60 MCQs) Quiz Instructions Select an option to see the correct answer instantly. 1. What happens to the power dissipated in a resistor when the r.m.s. current increases? A) It remains constant. B) It becomes zero. C) It increases. D) It decreases. Show Answer Correct Answer: C) It increases. 2. What is the configuration of components in a series LCR circuit? A) Parallel. B) Series. C) Mixed. D) None. Show Answer Correct Answer: B) Series. 3. An increase in which of the following factors will cause an increase in the inductive reactance of a circuit? A) Inductance and frequency. B) Resistance and voltage. C) Resistance and capacitive reactance. D) None of the above. Show Answer Correct Answer: A) Inductance and frequency. 4. What is the primary function of a resistor in an AC circuit? A) To increase current flow in the circuit. B) To store electrical energy for later use. C) To limit current and control voltage levels. D) To convert AC to DC voltage. Show Answer Correct Answer: C) To limit current and control voltage levels. 5. How does the length of the conductor affect the emf generated? A) Longer conductors generate more emf. B) Longer conductors generate less emf. C) Shorter conductors generate maximum emf. D) It has no effect on the emf. Show Answer Correct Answer: A) Longer conductors generate more emf. 6. What is the function of the fuse in a plug? A) To connect the appliance to the earth. B) To protect the appliance from excess current. C) To increase current. D) To decrease voltage. Show Answer Correct Answer: B) To protect the appliance from excess current. 7. What type of electric current moves from the positive polarity to a negative polarity and moves forward at all times? A) Direct Currents. B) Alternating Currents. C) All the above. D) None of the above. Show Answer Correct Answer: A) Direct Currents. 8. What happens to a light bulb when alternating current reverses direction? A) It stops glowing. B) It glows continuously. C) It flickers. D) It turns off. Show Answer Correct Answer: B) It glows continuously. 9. Equation of power factor A) Sin phi. B) Tan phi. C) Cot phi. D) Cos phi. Show Answer Correct Answer: D) Cos phi. 10. How does the use of AC impact electrical safety? A) AC can increase the risk of electric shock and requires proper safety measures to mitigate hazards. B) AC does not require any safety measures. C) AC is safer than DC in all situations. D) AC eliminates the risk of electric shock. Show Answer Correct Answer: A) AC can increase the risk of electric shock and requires proper safety measures to mitigate hazards. 11. The voltage drop in the power line is A) 2.8 kV. B) 2 kV. C) 3 kV. D) 1.7 kV. Show Answer Correct Answer: C) 3 kV. 12. The amount of electricity a capacitor can store is directly proportional to the A) Distance between the plates and inversely proportional to the plate area. B) Plate area and is not affected by the distance between the plates. C) Plate area and inversely proportional to the distance between the plates. D) None of the above. Show Answer Correct Answer: C) Plate area and inversely proportional to the distance between the plates. 13. Which will light a lamp more brightly, 12 V peak ac or 12 V steady dc? A) 12 V peak ac. B) 12 V steady dc. C) All the above. D) None of the above. Show Answer Correct Answer: B) 12 V steady dc. 14. The resistance of the ideal conductor is A) Very low. B) High. C) Medium. D) Very high. Show Answer Correct Answer: A) Very low. 15. Capacitance is measured in ..... A) Joules. B) Farads. C) Amperes. D) Henrys. Show Answer Correct Answer: B) Farads. 16. Voltage leads the current in an AC generators can be referred to A) Resistance. B) Capacitance. C) Inductance. D) None of the above. Show Answer Correct Answer: C) Inductance. 17. If frequency of AC source is doubled, the inductive reactance will: A) Become double. B) Remain same. C) Become four times. D) Become half. Show Answer Correct Answer: A) Become double. 18. Alternating current is the current which A) Changes in magnitude only. B) Changes in direction only. C) Changes both in magnitude and direction. D) Neither changes in magnitude nor changes in direction. Show Answer Correct Answer: C) Changes both in magnitude and direction. 19. Which device stores energy in electric field in AC circuit? A) Capacitor. B) Resistor. C) Inductor. D) Generator. Show Answer Correct Answer: A) Capacitor. 20. When an alternating emf flows through an unknown device. it is found that both alternating emf and alternating current are in phase with each other. Identify the device. A) Inductor L. B) Capacitor C. C) Resistor R. D) Both inductor and resistor. Show Answer Correct Answer: C) Resistor R. 21. Electric current that reverses its direction of flow in a regular pattern A) Voltage. B) Direct Current. C) Alternating Current. D) Parallel Circuit. Show Answer Correct Answer: C) Alternating Current. 22. What is the main principle behind the operation of an AC generator? A) Mechanical friction. B) Chemical reaction. C) Electromagnetic induction. D) Thermal conduction. Show Answer Correct Answer: C) Electromagnetic induction. 23. The Phase Angle between Current and Voltage in a LCR circuit is always A) Zero. B) $\pi$. C) $-\frac{\pi}{2}$. D) None of These. Show Answer Correct Answer: D) None of These. 24. The Phase Angle between Current and Voltage in a Resistance circuit is A) $\frac{\pi}{4}$. B) $\frac{-\pi}{2}$. C) 0. D) $+\frac{\pi}{2}$. Show Answer Correct Answer: C) 0. 25. What are the advantages of using AC over DC for power transmission? A) DC is preferred for reducing energy loss in power transmission. B) AC cannot be transformed to high voltages easily. C) AC is less efficient for long-distance transmission than DC. D) AC is advantageous for power transmission because it can be easily transformed to high voltages, reducing energy loss, and is more efficient for long-distance transmission. Show Answer Correct Answer: D) AC is advantageous for power transmission because it can be easily transformed to high voltages, reducing energy loss, and is more efficient for long-distance transmission. 26. Explain the relationship between resonance and frequency in AC circuits. A) Resonance occurs at a fixed frequency in AC circuits. B) Frequency in AC circuits is not related to resonance. C) Resonance only happens in DC circuits. D) Resonance in AC circuits happens at the frequency where inductive and capacitive reactances cancel each other out, resulting in a peak in current flow. Show Answer Correct Answer: D) Resonance in AC circuits happens at the frequency where inductive and capacitive reactances cancel each other out, resulting in a peak in current flow. 27. A transistor oscillator using a resonant circuit with an inductor L and a capacitor C in series produce oscillations of frequency f. If L is doubled and C is changed to 4C, the frequency will be A) 8f. B) $\frac{f}{2\sqrt{2}}$. C) F/2. D) F/4. Show Answer Correct Answer: B) $\frac{f}{2\sqrt{2}}$. 28. To reduce the resonant frequency in an LCR series circuit with a generator A) The generator frequency should be reduced. B) Another capacitor should be added in parallel to the first. C) The iron core of the inductor should be removed. D) Dielectric in the capacitor should be removed. Show Answer Correct Answer: B) Another capacitor should be added in parallel to the first. 29. What does the term 'reactance' refer to in A.C. circuits? A) Opposition to current flow. B) Power consumption. C) Opposition to A.C. current. D) Resistance to direct current. Show Answer Correct Answer: C) Opposition to A.C. current. 30. How does the use of transformers benefit AC power systems? A) They allow for easy conversion of AC to DC. B) They enable efficient voltage transformation for transmission and distribution. C) They increase the frequency of the current. D) They reduce the need for power stations. Show Answer Correct Answer: B) They enable efficient voltage transformation for transmission and distribution. 31. State whether the following statements is TRUE or FALSE;Visible light is not part of the spectrum. A) True. B) False. C) All the above. D) None of the above. Show Answer Correct Answer: B) False. 32. Average power in a purely resistive circuit A) VI sin phi. B) VI. C) VI cos phi. D) 0. Show Answer Correct Answer: B) VI. 33. What is the relationship between voltage and current in reducing energy losses in AC transmission? A) Higher voltage and higher current reduce losses. B) Higher voltage and lower current reduce losses. C) Lower voltage and higher current reduce losses. D) Lower voltage and lower current reduce losses. Show Answer Correct Answer: B) Higher voltage and lower current reduce losses. 34. In an AC circuit, what does the term 'mean voltage' refer to? A) The maximum voltage reached. B) The average voltage over a complete cycle. C) The peak voltage divided by two. D) The voltage at the midpoint of the cycle. Show Answer Correct Answer: B) The average voltage over a complete cycle. 35. Impedance in a LCR circuit at resonance A) 0. B) R. C) XL. D) Z. Show Answer Correct Answer: B) R. 36. What does AC smoothing mean? A) The process of inducing an emf (voltage) with a change in magnetic flux. B) Electric currents whose direction and magnitude change periodically depending on time are called alternating current. C) Steady current which delivers the same average power as the a.c. to a resistive load. D) Making a rectified current more steady (or smooth) by placing a capacitor in parallel with the resistor. Show Answer Correct Answer: D) Making a rectified current more steady (or smooth) by placing a capacitor in parallel with the resistor. 37. A 30-microfarad capacitor is in parallel with a 15-microfarad capacitor. The total capacitance is ..... A) 45. B) 30. C) 15. D) 100. Show Answer Correct Answer: A) 45. 38. What is an LCR circuit composed of? A) Inductor, Capacitor, Diode. B) Capacitor, Resistor, Transistor. C) Inductor, Capacitor, Resistor. D) Inductor, Resistor, Transistor. Show Answer Correct Answer: C) Inductor, Capacitor, Resistor. 39. The most common waveforms of ac is A) Triangular wave. B) Square wave. C) Complex wave. D) Sine wave. Show Answer Correct Answer: D) Sine wave. 40. What is the average value of current in a full-wave rectified circuit? A) Equal to peak value. B) Zero. C) Half the peak value. D) Twice the half-wave average. Show Answer Correct Answer: D) Twice the half-wave average. 41. L, C and R represent physical quantities inductance, capacitance and resistance, respectively. The combination representing dimension of frequency is A) $\left(LC\right)^{\frac{-1}{2}}$. B) $\frac{C}{L}$. C) LC. D) $\left(\frac{L}{C}\right)^{\frac{-1}{2}}$. Show Answer Correct Answer: A) $\left(LC\right)^{\frac{-1}{2}}$. 42. A charged 30 micro farad capacitor is connected to a 27mH inductor. The angular frequency of free oscillations of the circuit is A) 2.1 x 10$^{3}$ rad/s. B) 1.1 x 10$^{3}$ rad/s. C) 4.1 x 10$^{3}$ rad/s. D) 3.1 x 10$^{3}$ rad/s. Show Answer Correct Answer: B) 1.1 x 10$^{3}$ rad/s. 43. The relation between the direction of induced emf and the direction of motion of the conductor is A) Parallel. B) Perpendicular. C) Equal. D) Not related. Show Answer Correct Answer: B) Perpendicular. 44. What is the term for the current that does not perform any work in an A.C. circuit? A) Reactive current. B) Direct current. C) Wattless current. D) Active current. Show Answer Correct Answer: C) Wattless current. 45. If a sinusoidal wave has a frequency of 50 Hz with 30 A r.m.s current, which of the following equation represents the wave? A) 30 sin 50t. B) 84.84 sin 25t. C) 60 sin 25t. D) 42.42 sin 314.2t. Show Answer Correct Answer: D) 42.42 sin 314.2t. 46. How can phase difference be adjusted in AC circuits? A) Phase difference can be adjusted using capacitors, inductors, variable resistors, or phase-shifting transformers. B) Changing the voltage level of the circuit. C) Using only resistors. D) Adjusting the frequency of the power supply. Show Answer Correct Answer: A) Phase difference can be adjusted using capacitors, inductors, variable resistors, or phase-shifting transformers. 47. What is the effect of resistance on the Q-factor of a resonant circuit? A) Doubles Q-factor. B) Decreases Q-factor. C) Increases Q-factor. D) No effect. Show Answer Correct Answer: B) Decreases Q-factor. 48. The average value of alternating current for one complete cycle is A) Zero. B) 1. C) $\sqrt{2}$. D) None of these. Show Answer Correct Answer: A) Zero. 49. An electrical element X when connected to an alternating voltage source has current through it leading the voltage by $\pi$ A) Series LR ckt. B) Resistor. C) Capacitor. D) Inductor. Show Answer Correct Answer: C) Capacitor. 50. The induced emf in a closed coil of wire, according to Faraday's Law, is proportional to:I. The magnitude of the magnetic flux II. The magnetic flux density III. The number of turnsIV. The rate of change of magnetic flux A) I. B) II. C) II and III (. D) III and IV. E) IV. Show Answer Correct Answer: D) III and IV. 51. Why is ac current transfer more effective than dc current transfer over long distances? A) Due to the height of power lines. B) Due to the use of ac generators. C) Due to step-up and step-down transformers reducing I$^{2}$R losses. D) Due to very high voltages. Show Answer Correct Answer: C) Due to step-up and step-down transformers reducing I$^{2}$R losses. 52. What is the effect of increasing the capacitance in a capacitive AC circuit on the current? A) The current increases. B) The current becomes zero. C) The current remains the same. D) The current decreases. Show Answer Correct Answer: A) The current increases. 53. What is the phase difference in an AC circuit? A) The phase difference in an AC circuit is the angle by which the voltage and current waveforms differ, typically measured in degrees or radians. B) The phase difference is the maximum voltage in the circuit. C) The phase difference is the frequency of the AC signal. D) The phase difference is the total resistance in the circuit. Show Answer Correct Answer: A) The phase difference in an AC circuit is the angle by which the voltage and current waveforms differ, typically measured in degrees or radians. 54. What is the ratio of powers delivered by 20 V dc and 20 V peak ac to the same load? A) 0.5. B) 1. C) 20. D) 2. Show Answer Correct Answer: D) 2. 55. The power factor of LCR circuit at resonance is ..... A) Zero. B) 0.707. C) 0.5. D) 1. Show Answer Correct Answer: D) 1. 56. The above half wave form is created by an AC going into which circuit? A) Transformer. B) Single diode. C) Bridge rectifier. D) Voltage regulator. Show Answer Correct Answer: B) Single diode. 57. The waveform of alternating current/voltage is: A) Sinusoidal. B) Stright line. C) Cotangent. D) Curved. Show Answer Correct Answer: A) Sinusoidal. 58. When calculating power in a reactive or inductive AC circuit, the true power is A) More than apparent power. B) Less than the apparent power in a reactive circuit and more than the apparent power in an inductive circuit. C) Less than the apparent power. D) None of the above. Show Answer Correct Answer: C) Less than the apparent power. 59. Energy is measured by A) Kilo Watt. B) Kilo Volt. C) Watt. D) Watt.hr. Show Answer Correct Answer: D) Watt.hr. 60. A bridge rectifier requires at least ..... diode(s). A) 2. B) 1. C) 8. D) 4. Show Answer Correct Answer: D) 4. ← PreviousNext →Related QuizzesScience QuizzesClass 12 QuizzesClass 12 Physics (Part I) Chapter 7 Alternating Current Quiz 1Class 12 Physics (Part I) Chapter 7 Alternating Current Quiz 2Class 12 Physics (Part I) Chapter 7 Alternating Current Quiz 3Class 12 Physics (Part I) Chapter 7 Alternating Current Quiz 4Class 12 Physics (Part I) Chapter 7 Alternating Current Quiz 5Class 12 Physics (Part I) Chapter 7 Alternating Current Quiz 6Class 12 Physics (Part I) Chapter 7 Alternating Current Quiz 7Class 12 Physics (Part I) Chapter 7 Alternating Current Quiz 8 🏠 Back to Homepage 📘 Download PDF Books 📕 Premium PDF Books