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 1 🏠 Homepage 📘 Download PDF Books 📕 Premium PDF Books Class 12 Physics (Part I) Chapter 7 Alternating Current Quiz 1 (60 MCQs) Quiz Instructions Select an option to see the correct answer instantly. 1. A measurement taken from zero to the highest value obtained in either the positive or negative half of a sine wave would determine? . A) The peak to peak voltage. B) The peak voltage. C) The effective voltage. D) The average voltage. Show Answer Correct Answer: B) The peak voltage. 2. Transfer of electrical energy from one circuit to another without the aid of electrical connections A) Is called induction. B) Is called capacitance. C) Can cause excessive arcing and heat, and as a result is practical for use only with low voltages/amperages. D) None of the above. Show Answer Correct Answer: A) Is called induction. 3. Alternating current can not be measured by dc ammeter because A) Ac changes its direction. B) Ac cannot pass through dc ammeter. C) Ac is virtual. D) Average value of complete cycle is zero. Show Answer Correct Answer: D) Average value of complete cycle is zero. 4. A pure inductor of inductance 15 H is connected to an a.c.s source of frequency 100 Hz. If the r.m.s. value of the voltage is 12 V, what is the maximum instantaneous output power? A) 1.3 $\times10^{-3}W$. B) 1.5 $\times10^{-2}W$. C) 0 W. D) 1.5 W. Show Answer Correct Answer: B) 1.5 $\times10^{-2}W$. 5. In the transformer described (primary:2200 V, 5 A, 4000 turns; secondary:220 V output), what is the secondary current (ideal transformer)? A) 10 A. B) 50 A. C) 25 A. D) 5 A. Show Answer Correct Answer: B) 50 A. 6. What device is used to transform voltages in an a.c. system? A) Transformer. B) Rectifier. C) Inverter. D) Converter. Show Answer Correct Answer: A) Transformer. 7. In an LCR circuit if impedance is $\sqrt{2}$ A) Zero. B) $30^0$. C) $45^0$. D) $60^0$. Show Answer Correct Answer: C) $45^0$. 8. Complete the sentence:A cable is made up of two or three ..... covered by an outer layer of rubber or flexible plastic. A) Capacitors. B) Insulators. C) Conductors. D) Resistors. Show Answer Correct Answer: C) Conductors. 9. An inductor having negligible resistance and 50 mH self inductance and 500 pF capacitance are connected in AC circuit. The resonance frequency will be ..... A) 31.8 Hz. B) 31.8 GHz. C) 31.8 MHz. D) 31.8 kHz. Show Answer Correct Answer: D) 31.8 kHz. 10. Alternating current is transmitted to distant places A) At high voltage and Low current. B) At high voltage and high current. C) At low voltage and low current. D) At low voltage and high current. Show Answer Correct Answer: A) At high voltage and Low current. 11. In an AC circuit containing only a capacitor, current: A) Is in phase with voltage. B) Leads voltage by 90$^\circ$. C) Has zero phase difference at resonance. D) Lags voltage by 90$^\circ$. Show Answer Correct Answer: B) Leads voltage by 90$^\circ$. 12. What device generates alternating current by rotating a magnetic field? A) Transformer. B) Battery. C) Alternator. D) Rectifier. Show Answer Correct Answer: C) Alternator. 13. The time taken for one cycle of an alternating current is called the ..... A) Amplitude. B) Frequency. C) Period. D) Wavelength. Show Answer Correct Answer: C) Period. 14. Explain the concept of inductive reactance. A) Inductive reactance is the opposition to AC current in an inductor, increasing with frequency. B) Inductive reactance decreases with increasing frequency in a resistor. C) Inductive reactance is the same as capacitive reactance in an inductor. D) Inductive reactance is the resistance to DC current in a capacitor. Show Answer Correct Answer: A) Inductive reactance is the opposition to AC current in an inductor, increasing with frequency. 15. What role does inductive reactance play in AC circuits? A) Inductive reactance in AC circuits decreases with frequency. B) Inductive reactance in AC circuits opposes the change in current flow due to inductors and increases with frequency. C) Inductive reactance in AC circuits supports the change in current flow due to inductors. D) Inductive reactance in AC circuits has no effect on current flow. Show Answer Correct Answer: B) Inductive reactance in AC circuits opposes the change in current flow due to inductors and increases with frequency. 16. A homeowner wants to install a new AC-powered air conditioner. What should they consider to ensure safe installation? A) Use any available outlet regardless of its rating. B) Check the outlet voltage and current rating, use a dedicated circuit, and follow manufacturer instructions. C) Ignore the manufacturer's instructions. D) Use extension cords for permanent installation. Show Answer Correct Answer: B) Check the outlet voltage and current rating, use a dedicated circuit, and follow manufacturer instructions. 17. What is the total opposition of current flow in AC circuit? A) Resistance. B) Capacitance reactance. C) Inductive reactance. D) Impedance. Show Answer Correct Answer: D) Impedance. 18. The ac adapter for a laptop computer contains a transformer. The input of the adapter is the 120 volts from the ac wall outlet. The output from the transformer is 20 volts. What is the turns ratio of the transformer? A) 0.17. B) 6. C) 100. D) This cannot be determined without knowing how many turns one of the coils in the transformer has. Show Answer Correct Answer: B) 6. 19. Why should water be kept away from AC electrical outlets? A) Water increases resistance. B) Water can cause short circuits and electric shocks. C) Water makes appliances work faster. D) Water reduces voltage. Show Answer Correct Answer: B) Water can cause short circuits and electric shocks. 20. A transformer is used to light a 140 watt, 24 volt lamp from 240V ac mains. The current in the main cable is 0.44A. The efficiency of the transformer is A) 48%. B) 90%. C) 63.8%. D) 83.3%. Show Answer Correct Answer: D) 83.3%. 21. What is the value of the greatest induced EMF in either direction called? A) Peak-to-peak value. B) Average value. C) Instantaneous value. D) Peak value. Show Answer Correct Answer: D) Peak value. 22. The combination of resistance, capacitance and induntance is referred to A) Amplitude. B) Angular frequency. C) Impedance. D) Reactance. Show Answer Correct Answer: C) Impedance. 23. What is the unit of frequency for alternating current? A) Ohms. B) Volts. C) Amperes. D) Hertz. Show Answer Correct Answer: D) Hertz. 24. Which of the following is true about energy losses in AC transmission? A) Energy losses are higher in AC than in DC. B) Energy losses are lower in AC due to the ability to use high voltages. C) Energy losses are the same for both AC and DC. D) Energy losses are negligible in both AC and DC. Show Answer Correct Answer: B) Energy losses are lower in AC due to the ability to use high voltages. 25. The root mean square current ( $I_{rms}$ A) Effective. B) Least. C) Peak. D) Average. Show Answer Correct Answer: A) Effective. 26. Mean value of ac for half cycle is A) Zero. B) $\frac{i_0}{\sqrt{2}}$. C) $\frac{2i_0}{\pi}$. D) None. Show Answer Correct Answer: C) $\frac{2i_0}{\pi}$. 27. Unit of voltage is A) Volt. B) MA. C) Watt. D) Ampere. Show Answer Correct Answer: A) Volt. 28. UCLES N78/II/22; CIE J84/II/24. In an ideal transformer, the most important function of the soft-iron core is A) To reduce eddy currents. B) To improve the flux-linkage between the primary and secondary coils. C) To dissipate the heat generated by the two coils. D) To produce a uniform radial field in the two coils. Show Answer Correct Answer: B) To improve the flux-linkage between the primary and secondary coils. 29. AC frequency in Pakistan mains supply is: A) 25 Hz. B) 60 Hz. C) 100 Hz. D) 50 Hz. Show Answer Correct Answer: D) 50 Hz. 30. What is one of the main advantages of using alternating current (a.c.)? A) It produces less arcing and sparking on contacts. B) It is more efficient than d.c. C) It requires less maintenance. D) It is more environmentally friendly. Show Answer Correct Answer: A) It produces less arcing and sparking on contacts. 31. Select the correct phrase: A) In a capacitive circuit the voltage leads the current. B) In an inductive circuit the current lags the voltage. C) In a resistive circuit, the current and voltage are out of phase. D) In a capacitive circuit the current lags the voltage. Show Answer Correct Answer: B) In an inductive circuit the current lags the voltage. 32. Which of the following best describes the waveform of a single-phase AC? A) Sine wave. B) Triangle wave. C) Square wave. D) Sawtooth wave. Show Answer Correct Answer: A) Sine wave. 33. AC is converted from one level of voltage for transmission and then reduced to a different level of voltage for utilization by the end-user by using? . A) Transformers. B) Rectifiers. C) Generators. D) Inverters. Show Answer Correct Answer: A) Transformers. 34. In LCR circuit if resistance increases, quality factor A) Increases finitely. B) Decreases finitely. C) Remains constant. D) None of these. Show Answer Correct Answer: B) Decreases finitely. 35. Out of the following, choose the correct relation A) 1H= 1V/1A. B) 1H= 1A/1V. C) 1H= 1V/1As. D) 1H= 1V/1A/s. Show Answer Correct Answer: D) 1H= 1V/1A/s. 36. An alternating voltage has the equation V(t) = (150 sin 3881t) V, determine instantaneous voltage when t = 5 ms. A) 67.3 V. B) 75.5 V. C) 79.1 V. D) 80.9 V. Show Answer Correct Answer: C) 79.1 V. 37. Consider an RLC circuit that is driven by an AC applied voltage. At resonance, A) The peak voltage across the resistor is equal to the peak voltage across the inductor. B) The peak voltage across the capacitor is greater than the peak voltage across the inductor. C) The current is in phase with the driving voltage. D) The peak voltage across the inductor is greater than the peak voltage across the capacitor. Show Answer Correct Answer: C) The current is in phase with the driving voltage. 38. A resistor is connected to an AC power supply. On this circuit, the current A) Leads the voltage by 90$^\circ$. B) Lags the voltage by 90$^\circ$. C) Is in same phase with the voltage. D) None of the given answers. Show Answer Correct Answer: C) Is in same phase with the voltage. 39. What is the effect of inductance in an AC circuit? A) Increases resistance. B) Stores energy as heat. C) Stores energy in a magnetic field. D) Decreases voltage. Show Answer Correct Answer: C) Stores energy in a magnetic field. 40. What is the definition of alternating current (AC)? A) Alternating current (AC) is a current that never changes direction. B) Alternating current (AC) is a type of static electricity. C) Alternating current (AC) is an electric current that periodically reverses direction. D) Direct current (DC) flows in one direction only. Show Answer Correct Answer: C) Alternating current (AC) is an electric current that periodically reverses direction. 41. In an ideal 1:8 step-down transformer, the primary power is 10 kW and the secondary current is 25 A. The primary voltage is: A) 400 V. B) 25, 600 V. C) 50 V. D) 3200 V. Show Answer Correct Answer: D) 3200 V. 42. Describe the role of inductance in an AC circuit. A) Inductance has no effect on AC circuits and only applies to DC circuits. B) Inductance increases current flow without any phase shift. C) Inductance reduces the overall resistance in a circuit without affecting reactance. D) Inductance opposes changes in current, creates a phase shift, and contributes to reactance in AC circuits. Show Answer Correct Answer: D) Inductance opposes changes in current, creates a phase shift, and contributes to reactance in AC circuits. 43. How does the frequency affect the reactance of an inductor? A) The reactance of an inductor decreases with frequency. B) The reactance of an inductor increases with frequency. C) The reactance of an inductor is independent of the frequency applied. D) The reactance of an inductor remains constant regardless of frequency. Show Answer Correct Answer: B) The reactance of an inductor increases with frequency. 44. What is the significance of the root mean square (RMS) value in AC circuits? A) The RMS value represents the average power delivered by an AC circuit. B) The RMS value is irrelevant in AC circuits. C) The RMS value is the peak value of the AC signal. D) The RMS value is only applicable to DC circuits. Show Answer Correct Answer: A) The RMS value represents the average power delivered by an AC circuit. 45. How do transformers work in AC circuits? A) Transformers convert DC to AC power directly. B) Transformers only work with resistive loads. C) Transformers work by using electromagnetic induction to transfer energy between coils in an AC circuit. D) Transformers use mechanical gears to transfer energy. Show Answer Correct Answer: C) Transformers work by using electromagnetic induction to transfer energy between coils in an AC circuit. 46. Which of the following is true about capacitors in ac circuit? A) Instantaneous power is zero. B) Mean power is zero. C) The current decreases when frequency decreases. D) Voltage across capacitor leads current. Show Answer Correct Answer: B) Mean power is zero. 47. Explain the significance of RMS values in AC circuits. A) RMS values are significant in AC circuits as they represent the effective voltage or current, allowing for accurate power calculations and comparisons with DC systems. B) RMS values are only relevant for DC circuits. C) RMS values indicate the peak voltage in AC circuits. D) RMS values are used to measure resistance in circuits. Show Answer Correct Answer: A) RMS values are significant in AC circuits as they represent the effective voltage or current, allowing for accurate power calculations and comparisons with DC systems. 48. In a region of uniform magnetic induction $B=10^{-2}$ $\pi^2$ A) 200 mA. B) 6 mA. C) $4\\pi^2$. D) 30 mA. Show Answer Correct Answer: B) 6 mA. 49. What role does phase difference play in resonance circuits? A) At resonance, phase difference is always 90 degrees. B) Phase difference indicates the relationship between voltage and current; at resonance, it is zero, maximizing power transfer. C) Phase difference only affects the frequency of the circuit. D) Phase difference is irrelevant in resonance circuits. Show Answer Correct Answer: B) Phase difference indicates the relationship between voltage and current; at resonance, it is zero, maximizing power transfer. 50. Describe the relationship between voltage and current in an AC circuit. A) Impedance has no effect on the relationship between voltage and current. B) Voltage and current in an AC circuit are related through impedance, and they can be out of phase. C) Voltage and current are always in phase in an AC circuit. D) Current is independent of voltage in an AC circuit. Show Answer Correct Answer: B) Voltage and current in an AC circuit are related through impedance, and they can be out of phase. 51. Universally available power is A) (a)AC power. B) (b)DC power. C) All the above. D) None of the above. Show Answer Correct Answer: A) (a)AC power. 52. What occurs when the conductor is moved at an angle of 45$^\circ$ to the magnetic field lines? A) Emf is generated at a minimum level. B) Emf is generated at a moderate level. C) No emf is generated. D) Maximum positive emf is generated. Show Answer Correct Answer: B) Emf is generated at a moderate level. 53. In a coil of self inductance 5 H the rate of change of current is 2 As$^{-1}$. Than emf induced in the coil is A) -10 V. B) 5 V. C) -5 V. D) 10 V. Show Answer Correct Answer: A) -10 V. 54. An inductor of reactance 1 $\Omega$ and a resistor of 2 $\Omega$ are connected in series to the terminals of a 6 V (rms) AC source. The power dissipated in the circuit is A) 14.4 W. B) 8 W. C) 0 W. D) 12 W. Show Answer Correct Answer: A) 14.4 W. 55. Reactance of a capacitor of capacitance C$\mu$F for ac frequency $\frac{400}{\pi}$ A) $50\\mu F$. B) $100\\mu F$. C) $75\\mu F$. D) $25\\mu F$. Show Answer Correct Answer: A) $50\\mu F$. 56. What is the primary function of the stator in an AC generator? A) To rotate and produce a magnetic field. B) To provide a stationary magnetic field. C) To convert mechanical energy to electrical energy. D) To store electrical energy. Show Answer Correct Answer: B) To provide a stationary magnetic field. 57. How does the turns ratio affect the voltage in a transformer? A) The turns ratio only affects the current, not the voltage. B) The turns ratio has no effect on the voltage. C) The turns ratio directly affects the voltage by determining whether the transformer steps up or steps down the voltage. D) The turns ratio determines the frequency of the voltage output. Show Answer Correct Answer: C) The turns ratio directly affects the voltage by determining whether the transformer steps up or steps down the voltage. 58. In an AC circuit, what does the term 'phase' refer to? A) The type of load connected. B) The speed of the current. C) The position of the waveform relative to time zero or another waveform. D) The amount of current flowing. Show Answer Correct Answer: C) The position of the waveform relative to time zero or another waveform. 59. When an AC voltage is applied to an LCR circuit, then A) I and V are out of phase with each other in R. B) I and V are in phase in L with in C, they are out of phase. C) I and V are out of phase in both C and L. D) I and V are out of phase in L and in phase in C. Show Answer Correct Answer: C) I and V are out of phase in both C and L. 60. Transformers in which the primary and secondary voltages are 180 degrees out of phase are known as ..... A) Like-wound transformers. B) Unlike-wound transformers. C) Unequal transformers. D) Step-up transformers. Show Answer Correct Answer: B) Unlike-wound transformers. 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