Question E5B05:
What is the effect on the magnitude of pure reactance when it is converted to susceptance?  

Choices:  
A: It is unchanged  
B: The sign is reversed  
C: It is shifted by 90 degrees  
D: It is replaced by its reciprocal    

Correct Answer is  D: It is replaced by its reciprocal  

For a pure reactance $X$ (ohms), the corresponding susceptance $B$ (siemens) is:
$$Z = jX \quad\Rightarrow\quad Y = \frac{1}{Z} = \frac{1}{jX} = -\,\frac{j}{X} \;\Rightarrow\; B = \operatorname{Im}(Y) = -\frac{1}{X}$$
Therefore, the magnitude changes as:
$$|B| = \frac{1}{|X|}$$

Why D is correct (It is replaced by its reciprocal):
- The magnitude of susceptance is the reciprocal of the magnitude of reactance for a purely reactive element.

Why the others are incorrect:
- A: Unchanged — False. Only true if $|X| = 1\ \Omega$; generally $|B| = 1/|X|$.
- B: The sign is reversed — While $B = -1/X$ does flip sign (inductive: negative $B$, capacitive: positive $B$), the question asks about magnitude. Magnitude has no sign; it becomes the reciprocal.
- C: Shifted by 90 degrees — That refers to phase. Magnitude conversion is by reciprocity, not a phase shift.

Useful formulas and rules of thumb:
- Inductor: $X_L = \omega L$ (positive), $B_L = -\dfrac{1}{X_L} = -\dfrac{1}{\omega L}$
- Capacitor: $X_C = -\dfrac{1}{\omega C}$ (negative), $B_C = -\dfrac{1}{X_C} = \omega C$
- Purely reactive: $Y = 1/Z$ ⇒ invert the magnitude and flip the sign: $B = -1/X$, so $|B| = 1/|X|$.