*Question E6F04:
What is the photovoltaic effect?*  

*Correct Answer is  B: The conversion of light to electrical energy*  

### AI Response: (may contain errors)  

The photovoltaic effect is the process by which light is converted into electrical energy. This is the principle behind devices like solar cells, which generate electricity when exposed to sunlight.

### Explanation:

1. **Correct Answer (B): The conversion of light to electrical energy**
   - The photovoltaic effect occurs when photons (light particles) strike a material and transfer their energy to electrons, causing them to move and create an electric current. This is the fundamental principle used in solar panels to generate electricity from sunlight.

2. **Why the other choices are incorrect:**
   - **Choice A: The conversion of voltage to current when exposed to light**
     - This describes a photoconductive effect, not the photovoltaic effect. Photoconductive materials change their electrical resistance when exposed to light, affecting current flow, but this is not the same as generating electrical energy from light.
   
   - **Choice C: The effect that causes a photodiode to emit light when a voltage is applied**
     - This describes electroluminescence, which is the principle behind LEDs (Light Emitting Diodes). In this process, applying a voltage causes the diode to emit light, which is the opposite of the photovoltaic effect.
   
   - **Choice D: The effect that causes a phototransistor’s beta to decrease when exposed to light**
     - This describes a change in the characteristics of a phototransistor due to light exposure, but it does not involve the conversion of light to electrical energy. Instead, it affects the transistor's amplification factor (beta).

### Useful Formula:

- The basic operation of a photovoltaic cell can be described by the equation:
  $$ P = I \times V $$
  where:
  - $P$ is the power generated (in watts),
  - $I$ is the current (in amperes),
  - $V$ is the voltage (in volts).

This formula shows how the electrical power output of a photovoltaic cell is determined by the current and voltage produced when light is converted into electrical energy.