Ac current MCQ CEE MBBS ENTRANCE , Nepal Entrance Nepal Quiz

Ac current MCQ CEE MBBS ENTRANCE , Nepal Entrance Nepal Quiz

Posted by Nepal Quiz

الخميس، 31 أكتوبر 2024

_Physics

 

Alternating Current (AC)

Definition

Alternating Current (AC) is an electric current that reverses direction periodically. Unlike direct current (DC), where the flow of electric charge is unidirectional, AC changes its direction at regular intervals, which is typically measured in Hertz (Hz).

Characteristics of AC

• Waveform: AC is commonly represented as a sine wave, though other waveforms like square waves and triangular waves can also occur.
• Frequency: The frequency of AC indicates how many cycles it completes in one second. In Nepal, the standard frequency is 50 Hz.
• Voltage Levels: AC can be transformed to different voltage levels using transformers, making it suitable for long-distance power transmission.

Applications of AC

AC is widely used in power systems for residential, commercial, and industrial applications due to its efficient transmission over long distances. Household appliances such as refrigerators, air conditioners, and lighting systems typically operate on AC power.

Advantages of AC

• Efficient for power distribution over long distances.
• Can be easily transformed to different voltage levels.
• Most electrical appliances are designed to operate on AC.

Conclusion

Understanding AC is crucial for students studying electrical engineering and physics, as it forms the basis of most modern electrical systems.

1. In an AC circuit, the voltage is:

A) Constant
B) Varies sinusoidally
C) Always positive
D) None of the above

2. The peak value of an AC voltage is 100 V. What is its RMS value?

A) 70.7 V
B) 100 V
C) 141.4 V
D) 50 V

3. What is the frequency of an AC signal with a period of 0.02 seconds?

A) 20 Hz
B) 50 Hz
C) 100 Hz
D) 25 Hz

4. In an inductive AC circuit, the current:

A) Lags the voltage
B) Leads the voltage
C) Is in phase with the voltage
D) Is always zero

5. The impedance in an AC circuit is represented by the symbol:

A) R
B) Z
C) I
D) V

6. Which of the following components opposes the flow of AC current?

A) Resistor
B) Capacitor
C) Inductor
D) All of the above

7. The average power in an AC circuit is given by:

A) P = VI
B) P = VIcos(φ)
C) P = V²/R
D) P = I²R

8. What is the unit of inductance?

A) Henry
B) Ohm
C) Farad
D) Volt

9. In a capacitive AC circuit, the current:

A) Lags the voltage
B) Leads the voltage
C) Is in phase with the voltage
D) Is always zero

10. The phase difference between voltage and current in an ideal resistor is:

A) 0 degrees
B) 90 degrees
C) 180 degrees
D) 270 degrees

11. What is the formula for calculating reactance in a capacitor?

A) X_L = 2πfL
B) X_C = 1/(2πfC)
C) X = R + jX
D) X = VI

12. The power factor in an AC circuit is defined as:

A) cos(φ)
B) sin(φ)
C) tan(φ)
D) 1

13. What happens to the total impedance in a parallel AC circuit if one branch is removed?

A) It decreases
B) It increases
C) It stays the same
D) Cannot be determined

14. Which of the following describes the behavior of a transformer?

A) It increases current
B) It decreases voltage
C) It transfers electrical energy
D) All of the above

15. The root mean square (RMS) current is defined as:

A) I_peak / √2
B) I_peak
C) I_average
D) 2I_peak

16. In a series RLC circuit, the total impedance is given by:

A) Z = R + jX_C
B) Z = R + jX_L
C) Z = R + j(X_L - X_C)
D) Z = R - j(X_L - X_C)

17. What is the main advantage of using AC over DC for power transmission?

A) Easier to generate
B) Can be transformed to higher voltages
C) Less energy loss
D) All of the above

18. The inductive reactance of a coil is directly proportional to:

A) Frequency
B) Capacitance
C) Resistance
D) Voltage

19. The formula for calculating power in an AC circuit with a power factor is:

A) P = VI
B) P = VIcos(φ)
C) P = I²R
D) P = V²/R

20. What is the reactance of a 50 µF capacitor at a frequency of 100 Hz?

A) 31.8 Ω
B) 15.9 Ω
C) 318 Ω
D) 159 Ω

21. An alternating current is represented mathematically as:

A) I = I₀sin(ωt)
B) I = I₀cos(ωt)
C) Both A and B
D) None of the above

22. What does the term 'frequency' refer to in an AC circuit?

A) The voltage level
B) The rate of change of current
C) The number of cycles per second
D) The resistance value

23. The phase angle in an AC circuit is the angle between:

A) Voltage and current
B) Current and resistance
C) Voltage and resistance
D) None of the above

24. What type of waveforms are typically produced by an AC generator?

A) Square wave
B) Sine wave
C) Triangular wave
D) Sawtooth wave

25. In an AC circuit, which law relates voltage, current, and impedance?

A) Ohm's Law
B) Kirchhoff's Law
C) Faraday's Law
D) Coulomb's Law

26. A capacitor in an AC circuit serves to:

A) Store energy
B) Oppose changes in voltage
C) Phase shift the current
D) All of the above

27. The total power in a three-phase AC system is calculated using:

A) P_total = P_phase × 3
B) P_total = √3 × V × I
C) P_total = VI
D) None of the above

28. Which device is used to measure AC current?

A) Ammeter
B) Voltmeter
C) Ohmmeter
D) Wattmeter

29. What is the formula for calculating total capacitance in a series circuit?

A) C_total = C₁ + C₂
B) 1/C_total = 1/C₁ + 1/C₂
C) C_total = C₁C₂/(C₁ + C₂)
D) C_total = C₁C₂

30. The effect of frequency on the inductive reactance is:

A) Directly proportional
B) Inversely proportional
C) No effect
D) Exponential

31. Which of the following is a characteristic of AC power?

A) Voltage and current can change direction
B) It can be easily transformed to different voltage levels
C) It is used for long-distance power transmission
D) All of the above

32. In an RLC series circuit at resonance, the impedance is:

A) Minimum
B) Maximum
C) Zero
D) Equal to resistance

33. The power consumed in an inductive circuit can be calculated using:

A) P = VI
B) P = VIcos(φ)
C) P = V²/R
D) P = I²R

34. The phase relationship in an RLC circuit is primarily determined by:

A) Resistance
B) Capacitance
C) Inductance
D) All of the above

35. The peak current in an AC circuit is:

A) Always greater than RMS current
B) Always less than RMS current
C) Equal to RMS current
D) Depends on the load

36. The term 'reactive power' refers to:

A) Power consumed by resistive loads
B) Power that does no work
C) Power that can be measured in watts
D) None of the above

37. The time period of a waveform is the inverse of:

A) Amplitude
B) Frequency
C) Wavelength
D) Velocity

38. In a resistive AC circuit, the power factor is:

A) 0
B) 1
C) -1
D) Greater than 1

39. The formula for calculating total inductance in a series circuit is:

A) L_total = L₁ + L₂
B) L_total = L₁L₂/(L₁ + L₂)
C) 1/L_total = 1/L₁ + 1/L₂
D) None of the above

40. The term 'impedance' refers to:

A) Total resistance in a circuit
B) Total opposition to current flow
C) Only resistance in a circuit
D) None of the above

41. What happens to the current in an AC circuit as the frequency increases?

A) It decreases
B) It remains the same
C) It increases
D) Cannot be determined

42. What is the effect of increasing capacitance in an AC circuit?

A) Decreases the reactance
B) Increases the reactance
C) No effect
D) Increases the resistance

43. A 1000 Ω resistor and a 500 μF capacitor are in series with a 120 V AC supply. The current can be calculated using:

A) I = V/R
B) I = V/Z
C) I = VR
D) I = Z/V

44. In a purely capacitive circuit, the phase angle is:

A) 0 degrees
B) 90 degrees
C) 180 degrees
D) -90 degrees