This quiz works best with JavaScript enabled. Home > Class 12 > Class 12 Physics (Part I) Chapter 7 Alternating Current – Quiz 39 🏠 Homepage 📘 Download PDF Books 📕 Premium PDF Books Class 12 Physics (Part I) Chapter 7 Alternating Current Quiz 39 (25 MCQs) Quiz Instructions Select an option to see the correct answer instantly. 1. How does the phase angle in an AC circuit affect power consumption? A) Power consumption is solely dependent on voltage and not affected by phase angle. B) The phase angle affects power consumption by determining the relationship between voltage and current, influencing real power usage. C) A larger phase angle always increases power consumption. D) The phase angle has no impact on power consumption. Show Answer Correct Answer: B) The phase angle affects power consumption by determining the relationship between voltage and current, influencing real power usage. 2. The combined effect of resistance and reactance in AC circuit is called A) Inductance. B) Impedance. C) Capacitance. D) Conductance. Show Answer Correct Answer: B) Impedance. 3. How does phase difference affect the performance of AC motors? A) Phase difference only affects DC motors, not AC motors. B) Phase difference affects AC motor performance by influencing torque, efficiency, and potential overheating. C) Phase difference improves the lifespan of AC motors. D) Phase difference has no impact on AC motor performance. Show Answer Correct Answer: B) Phase difference affects AC motor performance by influencing torque, efficiency, and potential overheating. 4. In a purely resistive AC circuit, the instantaneous power is: A) Always zero. B) Always positive. C) Sometimes positive, sometimes negative. D) Maximum at current zero. Show Answer Correct Answer: B) Always positive. 5. In an ac circuit, peak value of voltage is 423 volts. Its effective voltage is ..... A) 400 volts. B) 323 volts. C) 300 volts. D) 340 volts. Show Answer Correct Answer: C) 300 volts. 6. How does the power factor affect the efficiency of an AC circuit? A) A high power factor always increases circuit voltage. B) A low power factor guarantees higher current flow. C) The power factor affects efficiency by determining how much of the supplied power is used for useful work; a low power factor reduces efficiency. D) Power factor has no impact on circuit performance. Show Answer Correct Answer: C) The power factor affects efficiency by determining how much of the supplied power is used for useful work; a low power factor reduces efficiency. 7. Syarat terjadinya frekuensi resonansi adalah ..... A) XL = XC. B) XL = XR. C) XR = XC. D) XL > XC. E) XL < XC. Show Answer Correct Answer: A) XL = XC. 8. What is a choke coil used for in AC circuits? A) Increase frequency. B) Block higher-frequency AC. C) Decrease voltage. D) Increase current. Show Answer Correct Answer: B) Block higher-frequency AC. 9. What device changes the voltage of an AC supply using electromagnetic induction? A) Rectifier. B) Transformer. C) Generator. D) Capacitor. Show Answer Correct Answer: B) Transformer. 10. The value of a given waveform at any instant time is termed as ..... A) Waveform. B) Instantaneous value. C) Cycle. D) Period. Show Answer Correct Answer: B) Instantaneous value. 11. Induced emf in a conductor of length l rotated with angular velocity w in a uniform magnetic field B is A) E = Blw. B) E = Bl$^{2}$w. C) E = Bl$^{2}$w/2. D) E = 2Bl$^{2}$w. Show Answer Correct Answer: C) E = Bl$^{2}$w/2. 12. How does a three-phase system benefit over a single-phase system? A) It requires less wiring. B) It provides a constant power delivery. C) It is cheaper to install. D) It is used only for small appliances. Show Answer Correct Answer: B) It provides a constant power delivery. 13. What is phasor diagram? A) A vector that rotates clockwise about its axis with constant angular velocity. B) A vector that rotates anticlockwise about its axis with constant angular velocity. C) A vector that rotates anticlockwise about its axis with constant angular acceleration. D) A vector that rotates clockwise about its axis with constant angular acceleration. Show Answer Correct Answer: B) A vector that rotates anticlockwise about its axis with constant angular velocity. 14. Same current is flowing in two alternating circuits. The first circuit contains only inductance and the other contains only a capacitor. If the frequency of the emf of AC is increased, the effect on the value of the current A) Increases in the first circuit and decreases in the other. B) Increases in both the circuits. C) Decreases in both the circuits. D) Decreases in the first circuit and increases in the other. Show Answer Correct Answer: D) Decreases in the first circuit and increases in the other. 15. Why is power factor correction important in electrical systems? A) To reduce energy losses, improve voltage stability, increase system capacity, and lower electricity costs. B) To maintain the power factor at an inefficient level. C) To worsen voltage stability and raise electricity costs. D) To increase energy losses and reduce system capacity. Show Answer Correct Answer: A) To reduce energy losses, improve voltage stability, increase system capacity, and lower electricity costs. 16. The peak current read from an oscilloscope trace is 5.25 A. What is the rms current? A) 7.42 V. B) 5.25 A. C) 3.71 A. D) 2.63 A. Show Answer Correct Answer: C) 3.71 A. 17. Angular displacement per unit time is ..... A) Frequency. B) Angular frequency. C) All the above. D) None of the above. Show Answer Correct Answer: B) Angular frequency. 18. A material that allows electrons to flow freely. A) Resistance. B) Electrical Conductor. C) Semiconductor. D) Direct Current. Show Answer Correct Answer: B) Electrical Conductor. 19. Unit of angular frequency is ..... A) Degree. B) Degrees per second. C) Second. D) None of the above. Show Answer Correct Answer: B) Degrees per second. 20. What is the effect of inductive reactance on the current in an AC circuit? A) Inductive reactance allows current to flow freely without any phase shift. B) Inductive reactance has no effect on the current in an AC circuit. C) Inductive reactance causes the current to lag behind the voltage, reducing the overall current flow. D) Inductive reactance increases the current flow in the circuit. Show Answer Correct Answer: C) Inductive reactance causes the current to lag behind the voltage, reducing the overall current flow. 21. What is the relationship between frequency and capacitive reactance? A) Constant. B) Directly proportional. C) Inversely proportional. D) No relationship. Show Answer Correct Answer: C) Inversely proportional. 22. Reactive power is always ..... A) Equal to true power. B) 90$^\circ$ out of phase with true power. C) Measured in ohms. D) Responsible for performing most of the work in a circuit. Show Answer Correct Answer: B) 90$^\circ$ out of phase with true power. 23. Which of the following is NOT a component of a three-pin plug? A) Live pin. B) Neutral pin. C) Earth pin. D) Plastic pin. Show Answer Correct Answer: D) Plastic pin. 24. The oscillations of a copper disc in a magnetic field are lightly damped because of A) Eddy Currents. B) Gravity. C) Inertia. D) None of these. Show Answer Correct Answer: A) Eddy Currents. 25. The impedance Z can be expressed as: A) $V_{rms}+I_{rms}$. B) $V_{rms}-I_{rms}$. C) $\frac{Vrms}{I_{rms}}$. D) $\frac{I_{rms}}{V_{rms}}$. Show Answer Correct Answer: C) $\frac{Vrms}{I_{rms}}$. ← PreviousNext →Related 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 8Class 12 Physics (Part I) Chapter 7 Alternating Current Quiz 9Class 12 Physics (Part I) Chapter 7 Alternating Current Quiz 10 🏠 Back to Homepage 📘 Download PDF Books 📕 Premium PDF Books