*Question G4E10:
Why should a series diode be connected between a solar panel and a storage battery that is being charged by the panel?*  

*Correct Answer is  B: To prevent discharge of the battery through the panel during times of low or no illumination*  

### AI Response: (may contain errors)  

A series diode is used between a solar panel and a storage battery to ensure that current flows only in one direction—from the solar panel to the battery. This is crucial for preventing the battery from discharging back through the solar panel when there is little or no sunlight.

### Explanation:

1. **Correct Answer (B):**  
   - **Preventing Discharge:** During times of low or no illumination, the voltage from the solar panel can drop below the battery voltage. Without a diode, this would allow current to flow from the battery back into the solar panel, discharging the battery. A diode blocks this reverse current, ensuring that the battery retains its charge.

2. **Why Other Choices Are Incorrect:**
   - **Choice A:** A diode does not regulate voltage. It only allows current to flow in one direction. Voltage regulation would require a different component, such as a voltage regulator.
   - **Choice C:** A diode does not limit current to a safe value. Current limiting would require a resistor or a current-limiting circuit.
   - **Choice D:** A diode does not prevent excessive voltage. Voltage protection would require a voltage regulator or a similar device to handle high illumination levels.

### Useful Concept:

- **Diode Functionality:** A diode allows current to flow in one direction (forward-biased) and blocks it in the opposite direction (reverse-biased). This is why it is effective in preventing reverse current flow from the battery to the solar panel.

By understanding the role of a diode in this context, you can see why it is essential for maintaining the charge of the battery when the solar panel is not generating sufficient voltage.