*Question E5A01:
What can cause the voltage across reactances in a series RLC circuit to be higher than the voltage applied to the entire circuit?*  

*Correct Answer is  A: Resonance*  

### AI Response: (may contain errors)  

In a series RLC circuit, the voltage across the reactances (inductor and capacitor) can be higher than the voltage applied to the entire circuit due to the phenomenon of resonance.

### Explanation:

1. **Why the correct answer is correct (Resonance):**
   - **Resonance** occurs in a series RLC circuit when the inductive reactance ($X_L$) equals the capacitive reactance ($X_C$). At this point, the circuit's impedance is minimized to just the resistance ($R$), and the current is maximized.
   - The formula for resonance is:
     $$ X_L = X_C $$
     where:
     - $X_L = 2\pi f L$ (inductive reactance)
     - $X_C = \frac{1}{2\pi f C}$ (capacitive reactance)
   - At resonance, the voltages across the inductor and capacitor can be much larger than the applied voltage due to the high current flowing through the circuit.

2. **Why the other choices are incorrect:**
   - **Capacitance (B):** While capacitance is a component of the circuit, it alone does not cause the voltage across reactances to exceed the applied voltage. It is the condition of resonance that causes this effect.
   - **Low quality factor (Q) (C):** A low quality factor indicates higher losses in the circuit, which would actually reduce the voltage across reactances rather than increase it.
   - **Resistance (D):** Resistance does not cause the voltage across reactances to exceed the applied voltage. In fact, higher resistance would dampen the circuit's response and reduce the voltage across the reactances.

### Useful Formula:

- The quality factor ($Q$) of a series RLC circuit is given by:
  $$ Q = \frac{1}{R} \sqrt{\frac{L}{C}} $$
  A higher $Q$ at resonance means a sharper peak in voltage across the reactances.

Understanding resonance and its effects on voltage in a series RLC circuit is crucial for the exam.