*Question G4C01:
Which of the following might be useful in reducing RF interference to audio frequency circuits?*  

*Correct Answer is  B: Bypass capacitor*  

### AI Response: (may contain errors)  

To reduce RF interference in audio frequency circuits, a bypass capacitor is often used. Here's why:

1. **Correct Answer: Bypass Capacitor**
   - A bypass capacitor provides a low impedance path to ground for high-frequency signals, effectively shunting RF interference away from sensitive audio circuits. This helps to prevent RF signals from being rectified and heard as noise in audio equipment.

2. **Why Other Choices Are Incorrect:**
   - **Bypass Inductor (A):** Inductors have high impedance at high frequencies, which makes them unsuitable for bypassing RF signals. Instead, they are often used in series to block RF interference.
   - **Forward-biased Diode (C):** A forward-biased diode conducts current and is not used for bypassing RF signals. It is typically used for rectification or switching applications.
   - **Reverse-biased Diode (D):** A reverse-biased diode blocks current flow and is used for voltage regulation or protection, not for bypassing RF signals.

3. **Useful Concept:**
   - The effectiveness of a bypass capacitor is determined by its impedance, which decreases with increasing frequency. The impedance \( Z \) of a capacitor is given by:
     $$ Z = \frac{1}{2\pi f C} $$
   - Where:
     - \( f \) is the frequency of the RF signal.
     - \( C \) is the capacitance.
   - As frequency \( f \) increases, the impedance \( Z \) decreases, making the capacitor more effective at shunting high-frequency interference to ground.

In summary, a bypass capacitor is the correct choice for reducing RF interference in audio circuits due to its ability to provide a low impedance path for high-frequency signals.