*Question G5A12:
What occurs in an LC circuit at resonance?*  

*Correct Answer is  D: Inductive reactance and capacitive reactance cancel*  

### AI Response: (may contain errors)  

In an LC circuit at resonance, the inductive reactance ($X_L$) and capacitive reactance ($X_C$) cancel each other out. This means that the total reactance of the circuit is zero, allowing the circuit to operate at its natural frequency.

### Correct Answer Explanation:
- **D: Inductive reactance and capacitive reactance cancel**  
  At resonance, the condition is given by:
  $$X_L = X_C$$  
  where:
  - $X_L = 2\pi f L$ (inductive reactance)
  - $X_C = \frac{1}{2\pi f C}$ (capacitive reactance)  
  When these two reactances are equal, they cancel each other, resulting in a purely resistive circuit at resonance. This allows maximum current to flow through the circuit.

### Incorrect Answer Explanations:
- **A: Current and voltage are equal**  
  This statement is misleading. While current and voltage can be in phase at resonance, they are not "equal" in value. The relationship between current and voltage depends on the impedance of the circuit.

- **B: Resistance is cancelled**  
  This is incorrect because resistance ($R$) does not cancel in an LC circuit. At resonance, the circuit can have a minimum impedance, but the resistive component remains and is crucial for determining power loss.

- **C: The circuit radiates all its energy in the form of radio waves**  
  While an LC circuit can radiate energy at resonance, it does not mean that all energy is radiated. Some energy is still dissipated as heat due to resistance in the circuit.

### Summary:
At resonance in an LC circuit:
- The inductive and capacitive reactances cancel each other out.
- The circuit behaves as a purely resistive circuit, allowing maximum current flow.
- The resonance condition is defined by the equality of $X_L$ and $X_C$. 

Understanding these concepts is essential for grasping the behavior of LC circuits in radio frequency applications.