*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)  

In the context of RF (radio frequency) applications, the primary cause of loss in film capacitors is the **skin effect**.

### Explanation:

1. **Correct Answer: Skin Effect**
   - At RF frequencies, the skin effect becomes significant. This phenomenon causes the current to flow primarily on the surface of the conductor, increasing the effective resistance and resulting in power loss. In capacitors, this effect can lead to increased losses at high frequencies.

2. **Why the Other Choices are Incorrect:**
   - **A: Inductance**
     - While inductance can affect the performance of capacitors at RF, it is not the primary cause of loss. Inductance mainly affects the resonant frequency and impedance characteristics rather than causing direct power loss.
   
   - **B: Dielectric Loss**
     - Dielectric loss is a factor in capacitors, but in film capacitors, it is generally low compared to other types of capacitors. It is not the primary cause of loss at RF frequencies.
   
   - **C: Self-discharge**
     - Self-discharge refers to the gradual loss of charge when a capacitor is not connected to a circuit. This is not a significant factor in RF applications and does not contribute to RF losses.

### Useful Formula:

- The skin depth, which is the depth at which the current density falls to $1/e$ of its value at the surface, is given by:
  $$ \delta = \sqrt{\frac{2\rho}{\omega \mu}} $$
  where:
  - $\delta$ = skin depth
  - $\rho$ = resistivity of the conductor
  - $\omega$ = angular frequency ($2\pi f$)
  - $\mu$ = permeability of the conductor

Understanding the skin effect and its impact on RF components is crucial for minimizing losses and optimizing performance in RF circuits.