Ohm's law expressed as E = IR

Options

A. can never be applied to AC
B. applies to AC in the same manner as to DC
C. always applies to AC circuits when Z is substituted for R
D. tells us that ` underset(eff)(E) `= 0.707 (` underset(max)(E) `) for AC

Answer

To solve the question regarding Ohm's law expressed as E = IR, we will analyze the given options and determine which one is correct based on the application of Ohm's law in AC circuits.

### Step-by-Step Solution:

1. **Understanding Ohm's Law**:
- Ohm's law states that the voltage (E) across a conductor is directly proportional to the current (I) flowing through it, with the resistance (R) being the proportionality constant. The formula is given as:
\[ E = I \cdot R \]

2. **Analyzing the Options**:
- **Option 1**: "Can never be applied to AC."
- This option is incorrect because Ohm's law can be applied to AC circuits under certain conditions.

- **Option 2**: "Applies to AC in the same manner as to DC."
- This option is also incorrect because while Ohm's law can be applied to AC, it does not apply in the same manner as it does in DC circuits due to the presence of reactance in AC circuits.

- **Option 3**: "Always applies to AC circuit when Z is substituted for capital R."
- This option is correct. In AC circuits, we use impedance (Z) instead of resistance (R) when applying Ohm's law. Impedance takes into account both resistance and reactance.

- **Option 4**: "Tells us that E effective is equal to 0.707 E maximum for AC."
- This option is partially correct but does not directly address the application of Ohm's law itself.

3. **Conclusion**:
- The correct option is **Option 3**: "Always applies to AC circuit when Z is substituted for capital R." This is valid under the condition of resonance in an LCR circuit where the inductive reactance (X_L) equals the capacitive reactance (X_C), leading to the impedance (Z) being equal to the resistance (R).

### Final Answer:
The correct option is **Option 3**.

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