*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 phenomenon that can cause the voltage across reactances (inductors and capacitors) to be higher than the total applied voltage is known as resonance.

### Correct Answer: A: Resonance

1. **Why Resonance is Correct:**
   - At resonance, the inductive reactance ($X_L$) and capacitive reactance ($X_C$) are equal in magnitude but opposite in phase. This results in the circuit having a very high impedance, which can lead to a significant increase in the voltage across the reactances.
   - The formula for the resonant frequency ($f_0$) is given by:
     $$
     f_0 = \frac{1}{2\pi\sqrt{LC}}
     $$
   - At this frequency, the voltage across the inductor ($V_L$) and the capacitor ($V_C$) can be much greater than the source voltage ($V_{source}$) due to the energy oscillating between the inductor and capacitor.

### Why the Other Choices are Incorrect:

2. **B: Capacitance**
   - While capacitance affects the reactance of the capacitor, it does not inherently cause the voltage across the reactance to exceed the total voltage. The voltage across a capacitor is determined by the charge and capacitance, but it does not lead to the condition described in the question.

3. **C: Low quality factor (Q)**
   - A low quality factor indicates that the circuit has higher resistive losses and is less selective at resonance. This means that the voltage across the reactances would not be significantly higher than the applied voltage, as energy is dissipated rather than stored.

4. **D: Resistance**
   - Resistance in the circuit causes energy loss in the form of heat and does not contribute to the increase in voltage across the reactances. In fact, higher resistance would typically lower the overall voltage across the reactances due to voltage drop.

### Summary:
- At resonance, the reactances can cause voltages to exceed the applied voltage due to the phase relationship and energy storage in the circuit.
- Other factors like capacitance, low Q, and resistance do not create the same effect and can actually dampen the voltage across the reactances.