Alternating current may be termed as 'wattless' in case of

Options

A. All series LR circuits
B. All series RC circuits
C. All series LC circuits
D. Series resonant LCR circuits

Answer

To determine when alternating current (AC) may be termed as 'wattless', we can analyze the relationship between current, voltage, and the phase difference between them. Here’s a step-by-step solution:

### Step 1: Understand the concept of 'wattless' current
- **Wattless current** refers to a situation where the average power consumed in the circuit is zero. This occurs when the phase difference between the current and voltage is 90 degrees.

**Hint**: Remember that power in an AC circuit is calculated using the formula \( P = V \times I \times \cos(\phi) \), where \( \phi \) is the phase difference.

### Step 2: Analyze the phase difference
- In an AC circuit, if the phase difference between the current (I) and voltage (V) is 90 degrees, then \( \cos(90^\circ) = 0 \). Therefore, the average power \( P \) becomes zero.

**Hint**: The cosine of 90 degrees is crucial in determining the average power.

### Step 3: Identify the circuit type
- This scenario typically occurs in **series LC circuits** (inductive and capacitive). In such circuits, the inductive reactance (VL) and capacitive reactance (VC) can cancel each other out, leading to a situation where the total voltage leads or lags the current by 90 degrees.

**Hint**: Recall that in LC circuits, the reactances can be equal and opposite, resulting in a phase difference of 90 degrees.

### Step 4: Conclusion about wattless current
- Since the average power consumed in a series LC circuit is zero due to the 90-degree phase difference, we can conclude that the alternating current in such a circuit is termed as 'wattless'.

**Hint**: Focus on the characteristics of series LC circuits to understand why they lead to wattless current.

### Final Answer
- Alternating current may be termed as 'wattless' in case of **series LC circuits**.