ECAT Entry Test Physics Alternating Current MCQs

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Alternating Current, Current Production, Current Waveform, Average Value of AC, AC Circuit Containing Resistance Only.

Dive into the essential concepts of Physics Alternating Current with Nokryan.com! Alternating current AC is one of the basic building blocks of electrical engineering, used to provide power to homes, industries, and modern technologies. It is essential for students who are preparing for entry tests such as ECAT to understand its principles, waveform behavior, and circuit characteristics.

ECAT Entry Test Physics Alternating Current MCQs

Introduction to Alternating Current (AC)

Alternating current (AC) alternates its direction of flow (as opposed to direct current [DC], which flows in a single direction). Most power systems option for AC as it is more efficient in transmitting power over long distances, and transformers can be used to easily step up and step down the voltage.

Current Production and AC Waveform

Alternating current is primarily generated using AC generators, which transform mechanical energy into electrical energy. The resulting voltage follows a sinusoidal waveform, meaning it oscillates symmetrically between positive and negative values. The highest point in the cycle is called the peak value, while the time taken for a full cycle is the time period (T).

Key Parameters in Physics Alternating Current

  1. Root Mean Square (RMS) Value: AC is commonly measured using its RMS value, which represents its effective power. The RMS value of an AC signal is 0.707 times its peak value.
  2. Average Value of AC: The average of an AC waveform over a full cycle is zero. However, over a half-cycle, the average value is 0.637 times the peak value.
  3. Frequency and Phase Angle: Frequency is the number of cycles per second, measured in hertz (Hz). The phase angle describes the position of the waveform relative to time.

AC Circuit Containing Resistance Only

When an AC circuit contains only resistance, such as a resistor, the voltage and current remain in phase, meaning their peaks and zero crossings occur simultaneously. The current in a pure resistive AC circuit is given by Ohm’s Law (V = IR), similar to a DC circuit.

Physics Alternating Current MCQs for ECAT Preparation

For students aiming to excel in ECAT Physics, practicing multiple-choice questions is essential. Below are sample Physics Alternating Current MCQs to reinforce learning

1. The most common source of alternating voltage is ?

  • AC generatorcorrect
  • Motor
  • Transformer
  • Both A & B
  • Both A & C

2. The alternating voltage or current is actually measured by ?

  • Its RMS value
  • Square root of its mean square value
  • Peak value
  • Instantaneous value
  • Both A & Bcorrect

3. The highest value reached by the voltage or current ?

  • In quarter cycle is called instantaneous value
  • None of these
  • In one cycle is called peak valuecorrect
  • In half cycle is called peak-to-peak value
  • In half cycle is called instantaneous value

4. The phase at the negative peak of an A. C. cycle is ?

  • 90º
  • 270ºcorrect
  • 180º
  • 0º
  • 360º

5. Peak value of alternating current is ?

  • Equal to its RMS value
  • One of its instantaneous valuescorrect
  • None of these
  • The same as its peak-to-peak value
  • Both B and C

6. The entire waveform of sinusoidal voltage is actually a set of all the ?

  • Instantaneous values which exist during a period Tcorrect
  • RMS values
  • Peak-to-peak values
  • None of tehse
  • Average values which exist during a period T/2

7. A sinusoidally alternating voltage or current can be graphically represented by a ?

  • None of these
  • Clockwise rotating vector
  • Anti clock wise voltage vectorcorrect
  • Vector
  • Rotating vector

8. Nowadays, most of the electrical energy is produced by A.C. generators using ?

  • Solar energy
  • Both B & D
  • Hydal watercorrect
  • Biomass
  • Geothrmal energy

9. Unless stated otherwise, when we speak of A.C. meter reading, we usually mean ?

  • Instantaneous value
  • Peak-to-peak value
  • RMS valuecorrect
  • Both A & C
  • Peak value

10. The RMS value of alternating voltage is ?

  • 0.7 times the peak valuecorrect
  • 0.5 times the peak value
  • None of these
  • 0.7 times the instantaneous value
  • Equal to maximum voltage

11. The waveform of alternating voltage is a ?

  • Sinusoidalcorrect
  • Rectangular
  • None of these
  • Saw-tooth
  • Square

12. The time interval during which source changes its polarity once is knows as ?

  • Quarter the time period
  • Half the time period
  • None of these
  • Two third of the time period
  • Time period Tcorrect

13. If we connect an A.C. voltmeter to read A.C. voltage, it would read its ?

  • Both B and C
  • RMS valuecorrect
  • Instantaneous value
  • Value averaged over a cycle
  • Zero

14. If 250V is the RMS value of alternating voltage, then its peak value V, will be ?

  • 400 V
  • 175 V
  • Zero
  • 250 V
  • 353.5 Vcorrect

15. The length of the rotating vector (on a certain scale) represents the ?

  • Instantaneous value of alternating quantity
  • RMS value of a alternating quantity
  • Either A or Bcorrect
  • Peak value of alternating quantity
  • Either B or C

16. Alternating current is produced by a voltage source which polarity ?

  • Remains the same
  • Keeps on reversing with time
  • Reverses after period T
  • Both C & Dcorrect
  • Reverses after every time interval T/2

17. Alternating current can be transmitted ?

  • To long distance at very low costcorrect
  • To long distance at very high cost
  • At very low cost
  • To long distance

18. The magnitude of alternating voltage V ?

  • Always increases
  • None of these
  • Remains constant
  • Always decreases
  • Des not remain constantcorrect

19. If we connect an ordinary DC ammeter to measure alternating current, it would measure its ?

  • Value averaged over a cyclecorrect
  • RMS value
  • Instantaneous value
  • Either B or C

20. The sum of positive and negative peak value) i,e., p-p value) is called ?

  • None of these
  • Instantaneous value
  • RMS value
  • Peak-to-peak valuecorrect
  • Peak value

21. The wave form of alternating voltage is the graph between ?

  • Either B or D
  • Voltage along y-axis and time along x-axiscorrect
  • Voltage along x-axis and along y-axis
  • Current and time
  • Voltage and current

22. The phase at the positive peak of an A.C cycle is ?

  • 0º
  • 90ºcorrect
  • 360
  • 270º
  • 180º

23. The peak-to-peak value of alternating voltage is ?
A = 2Vº
B = V º
C = Vº /2
D = 4V º
E = None of these

  • D
  • B
  • C
  • Acorrect

24. The instantaneous value of alternating current may be ?

  • The same as its peak valuecorrect
  • The same as its RMS value
  • Greater than its RMS value
  • None of tehse
  • Any of these

25. The points where the waveform of an A.C. cycle cross  the time axis corresponds to phase ?

  • 0º
  • π/2 and 3π/2
  • 90º
  • 180º
  • 0 and πcorrect

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