CH 8: Alternating current
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Questions and Answers

What is the relationship between average power (Pave), RMS current (Irms), and RMS voltage (Vrms) in a purely resistive AC circuit?

  • Pave = Irms^2 / Vrms
  • Pave = Irms^2 * Vrms
  • Pave = Irms / Vrms
  • Pave = Irms * Vrms (correct)

What is the relationship between frequency (f) and period (T) in an AC circuit?

  • T = f^2
  • T = 1/f (correct)
  • T = 1/f^2
  • T = f

Which formula can be used to calculate the average power (Pave) in a resistive AC circuit, given the RMS current (Irms) and resistance (R)?

  • Pave = Irms * R
  • Pave = Irms / R
  • Pave = Irms^2 / R
  • Pave = Irms^2 * R (correct)

Why is AC preferred over DC for power transmission over long distances?

<p>AC can be easily stepped up and down in voltage, reducing energy loss. (A)</p> Signup and view all the answers

Which of the following devices operates exclusively with AC?

<p>Transformers (C)</p> Signup and view all the answers

Which of the following is NOT an advantage of alternating current (AC) over direct current (DC)?

<p>AC is more efficient for long-distance power transmission due to lower voltage drop. (D)</p> Signup and view all the answers

In an AC circuit, the voltage and current vary over time in a sinusoidal pattern. At what points in the cycle do the maximum values (Vmax and Imax) occur?

<p>At the peaks of the cycle (B)</p> Signup and view all the answers

What is the root mean square (RMS) voltage (Vrms) defined as?

<p>The equivalent DC voltage that would produce the same amount of heat in a resistor as the AC voltage. (A)</p> Signup and view all the answers

In the context of AC circuits, what does the term 'transformability' refer to?

<p>The ability to change the voltage level of the AC signal using transformers. (C)</p> Signup and view all the answers

Which of the following statements about the RMS current (Irms) is correct?

<p>It is the equivalent DC current that would produce the same amount of heat in a resistor as the AC current. (C)</p> Signup and view all the answers

What does the period (T) of an AC signal represent?

<p>Time taken to complete one cycle (B)</p> Signup and view all the answers

How does the frequency (f) of an AC signal relate to the number of cycles?

<p>It is directly proportional to the number of cycles (A)</p> Signup and view all the answers

What is the role of transformers in AC circuits for power transmission?

<p>Step up or down voltage (D)</p> Signup and view all the answers

How does average power calculation differ between DC and resistive AC circuits?

<p>In AC, average power depends on resistance and RMS current (C)</p> Signup and view all the answers

Why is understanding RMS values important when dealing with AC circuits?

<p>To analyze the sinusoidal variation (C)</p> Signup and view all the answers

Which parameter indicates the actual power used or dissipated in a purely resistive circuit?

<p>$P_{ave}$ (A)</p> Signup and view all the answers

What is the standard frequency of AC power in South Africa?

<p>50 Hz (B)</p> Signup and view all the answers

How does the utilization of RMS values aid in solving problems related to AC circuits?

<p>To simplify calculations compared to DC circuits (C)</p> Signup and view all the answers

In an AC circuit, what is the phase relationship between the voltage and current waveforms?

<p>The phase relationship depends on the circuit components (D)</p> Signup and view all the answers

What is the significance of using RMS values for AC voltage and current?

<p>RMS values are used to compare the heating effects of AC with DC (D)</p> Signup and view all the answers

What is the relationship between the RMS voltage (Vrms) and the maximum voltage (Vmax) in an AC circuit?

<p>Vrms = √2 * Vmax (B)</p> Signup and view all the answers

Why is AC preferred over DC for long-distance power transmission?

<p>AC can be easily stepped up or down in voltage using transformers (A)</p> Signup and view all the answers

In an AC circuit, what is the period (T) defined as?

<p>The time taken for one complete cycle of the waveform (C)</p> Signup and view all the answers

What is the primary reason for using high voltages in long-distance power transmission?

<p>All of the above (D)</p> Signup and view all the answers

What is the relationship between the frequency (f) and the period (T) of an AC waveform?

<p>f = 1/T (D)</p> Signup and view all the answers

In a purely resistive AC circuit, what is the phase relationship between the voltage and current waveforms?

<p>The voltage and current are in phase (A)</p> Signup and view all the answers

What is the primary advantage of using AC in electric generators and motors?

<p>AC allows for easy changing of magnetic fields (D)</p> Signup and view all the answers

What is the significance of using high voltages in AC power transmission?

<p>Reduces current needed for the same power transfer (A)</p> Signup and view all the answers

Why is it easier to convert AC to DC compared to converting DC to AC?

<p>AC involves changing magnetic fields (C)</p> Signup and view all the answers

What is the main advantage of using transformers in AC circuits?

<p>Step up or down voltage levels (D)</p> Signup and view all the answers

Which statement best describes Root Mean Square (RMS) values in AC circuits?

<p>They allow comparison to constant DC values (D)</p> Signup and view all the answers

What do Vmax and Imax represent in an AC circuit?

<p>Peak voltage and current values (D)</p> Signup and view all the answers

In which scenario would thinner wires be used for power transmission?

<p>High-voltage AC transmission (B)</p> Signup and view all the answers

How do RMS Current (Irms) and RMS Voltage (Vrms) simplify analysis in AC circuits?

<p>By facilitating comparisons with DC circuits (A)</p> Signup and view all the answers

What happens to voltage and current values at every half cycle of an AC waveform?

<p>Both values are zero (A)</p> Signup and view all the answers

Which statement best explains why high-voltage AC transmission reduces energy loss?

<p>Reduced current leads to lower heating losses in power lines. (A)</p> Signup and view all the answers

Which of the following formulas can be used to calculate the average power ($P_{ave}$) in a purely resistive AC circuit, given the RMS current ($I_{rms}$) and resistance ($R$)?

<p>$P_{ave} = I_{rms}^2 R$ (D)</p> Signup and view all the answers

What is the relationship between the frequency ($f$) and the period ($T$) of an AC waveform?

<p>$f = 1 / T$ (C)</p> Signup and view all the answers

Why is AC preferred over DC for long-distance power transmission?

<p>AC can be easily stepped up and down in voltage, reducing energy loss. (A)</p> Signup and view all the answers

What is the significance of using RMS values for AC voltage and current?

<p>RMS values allow for direct comparison to DC values. (B)</p> Signup and view all the answers

In an AC circuit, what is the phase relationship between the voltage and current waveforms for a purely resistive load?

<p>The voltage and current are in phase. (D)</p> Signup and view all the answers

What is the primary advantage of using AC in electric generators and motors?

<p>AC can be easily transformed to different voltage levels. (C)</p> Signup and view all the answers

In the context of AC circuits, what does the term 'transformability' refer to?

<p>The ability to change the voltage and current levels of an AC signal. (C)</p> Signup and view all the answers

What is the relationship between the RMS voltage ($V_{rms}$) and the maximum voltage ($V_{max}$) in an AC circuit?

<p>$V_{rms} = \sqrt{2} V_{max}$ (C)</p> Signup and view all the answers

What is the standard frequency of AC power in South Africa?

<p>50 Hz (D)</p> Signup and view all the answers

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