Question
Which point in Figure E5-1 best represents the impedance of a series circuit consisting of a 300-ohm resistor and an 18-microhenry inductor at 3.505 MHz?
Answer Options
- A) Point 1
- B) Point 3
- C) Point 7
- D) Point 8
Correct Answer: B
Explanation
To determine the impedance, we first calculate the inductive reactance (X_L) and then express the impedance in rectangular form (Z = R + jX_L). The inductance is L = 18 \times 10^{-6} \text{ H} and the frequency is f = 3.505 \times 10^6 \text{ Hz}. X_L = 2\pi f L = 2\pi (3.505 \times 10^6)(18 \times 10^{-6}) \approx 396.4 \Omega The impedance is Z = 300 + j396.4 \Omega. This point must be plotted where R = 300 on the positive X-axis and X is approximately +400 on the positive Y-axis.
Consulting Figure E5-1, the horizontal axis scale is resistive (R), and the vertical axis scale is reactive (X). Point 3 is located at approximately R=+300 and X \approx +400. Therefore, Point 3 best represents the impedance of this inductive circuit.
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