*Question E5D08:
What is the primary cause of loss in film capacitors at RF?*  

*Correct Answer is  D: Skin effect*  

### AI Response: (may contain errors)  

The primary cause of loss in film capacitors at RF (radio frequency) is primarily due to the skin effect. Let's break down the correct answer and the other choices:

### Correct Answer: Skin Effect
- **Explanation**: At high frequencies, the current tends to flow near the surface of the conductor rather than through its entire cross-section. This phenomenon is known as the skin effect. In film capacitors, this can lead to increased resistance and energy loss, as the effective area for current flow is reduced. The skin depth ($\delta$) can be calculated using the formula:

$$
\delta = \sqrt{\frac{2}{\omega \mu \sigma}}
$$

where:
- $\omega$ = angular frequency ($2\pi f$, with $f$ being the frequency in hertz)
- $\mu$ = permeability of the material
- $\sigma$ = conductivity of the material

### Why the Other Choices are Incorrect:
- **A: Inductance**: While inductance can cause losses in capacitors, it is not the primary cause of loss in film capacitors at RF. Inductance affects the capacitor's ability to operate at high frequencies but does not directly account for energy loss in the same way as skin effect.

- **B: Dielectric Loss**: Dielectric loss refers to the energy lost as heat in the dielectric material of the capacitor due to its inherent properties. While this can be a factor, it is not the primary cause of loss at RF frequencies compared to the skin effect.

- **C: Self-discharge**: Self-discharge is the process by which a capacitor loses its charge over time due to leakage currents. This is more relevant in the context of energy storage and retention rather than losses during operation at RF frequencies.

### Summary
- The skin effect is the primary cause of loss in film capacitors at RF due to the concentration of current near the surface of conductors.
- Inductance, dielectric loss, and self-discharge are factors but do not primarily account for RF losses in film capacitors. 

Understanding these concepts will help you grasp the behavior of capacitors in RF applications and prepare effectively for the Extra Class exam.