*Question E5A07:
What is the magnitude of the current at the input of a parallel RLC circuit at resonance?*  

*Correct Answer is  A: Minimum*  

### AI Response: (may contain errors)  

At resonance in a parallel RLC circuit, the behavior of the circuit changes significantly. Let's break down the question and the answer.

### Correct Answer: Minimum

1. **Why the correct answer is correct:**
   - At resonance, the inductive reactance ($X_L$) and capacitive reactance ($X_C$) are equal, which means they cancel each other out. This results in the circuit drawing the least amount of current from the source because the impedance of the circuit is at its maximum. 
   - The total impedance ($Z$) of a parallel RLC circuit at resonance can be expressed as:
     $$ Z = \frac{R}{1 + \left(\frac{X_L - X_C}{R}\right)^2} $$
   - Since $X_L = X_C$ at resonance, the impedance becomes very high, leading to a minimum current drawn from the source.

### Why the Other Choices are Incorrect:

2. **Choice A: Minimum**
   - This is the correct answer, as explained above.

3. **Choice B: Maximum**
   - This choice is incorrect because, at resonance, the current is not at its maximum. Instead, the cancellation of reactances leads to a higher impedance, resulting in lower current.

4. **Choice C: R/L**
   - This choice suggests a specific ratio of resistance to inductance, which does not apply to the current at resonance. The current is not defined by this ratio in a parallel RLC circuit.

5. **Choice D: L/R**
   - Similar to choice C, this ratio does not represent the current at resonance. The current is influenced by the overall impedance of the circuit rather than a simple ratio of inductance to resistance.

### Summary:
- At resonance in a parallel RLC circuit, the current is at a minimum due to the cancellation of inductive and capacitive reactances, resulting in maximum impedance. Understanding this concept is crucial for the Extra Class exam and practical applications in amateur radio.