*Question E5D06:
What parasitic characteristic creates an inductor’s self-resonance?*  

*Correct Answer is  D: Inter-turn capacitance*  

### AI Response: (may contain errors)  

In an inductor, self-resonance occurs when the inductive reactance and capacitive reactance within the inductor cancel each other out, creating a resonant frequency. This is primarily due to:

### Correct Answer: Inter-turn capacitance

- **Inter-turn capacitance** is the capacitance that exists between the turns of the coil in an inductor. As the frequency increases, this capacitance can resonate with the inductance, leading to self-resonance. The self-resonant frequency is where the inductive and capacitive reactances are equal in magnitude but opposite in phase, effectively canceling each other out.

### Why the Other Choices are Incorrect:

- **Skin effect (Choice A):** This is a phenomenon where alternating current tends to flow near the surface of a conductor at higher frequencies, increasing the effective resistance. It does not directly cause self-resonance in an inductor.

- **Dielectric loss (Choice B):** This refers to the energy lost in a dielectric material when it is subjected to a varying electric field. It is more relevant to capacitors and does not cause self-resonance in inductors.

- **Coupling (Choice C):** This refers to the transfer of energy between two circuits or components. While coupling can affect circuit behavior, it is not the cause of an inductor's self-resonance.

### Useful Formula:

The self-resonant frequency ($f_{\text{res}}$) of an inductor can be approximated by:

$$
f_{\text{res}} = \frac{1}{2\pi \sqrt{L \cdot C}}
$$

where:
- $L$ is the inductance,
- $C$ is the inter-turn capacitance.

Understanding this concept helps in designing circuits to avoid unwanted resonances that can affect performance.