*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 a fundamental principle in solar energy technology. Let's break down the question and the choices:

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

- **Explanation**: The photovoltaic effect refers to the process by which certain materials, typically semiconductors like silicon, generate an electric current when they absorb light. When photons from light strike the material, they can excite electrons, allowing them to flow and create an electric current. This is the basic principle behind solar cells.

### Why the Other Choices are Incorrect:

- **A: The conversion of voltage to current when exposed to light**  
  - This statement is misleading. The photovoltaic effect specifically involves the conversion of light (photons) into electrical energy (current), not the conversion of voltage to current. Voltage is a measure of electric potential, not a direct result of light exposure.

- **C: The effect that causes a photodiode to emit light when a voltage is applied**  
  - This describes the operation of a light-emitting diode (LED) or a photodiode in reverse bias, where it emits light when current flows through it. This is not related to the photovoltaic effect, which focuses on generating electricity from light, not emitting light.

- **D: The effect that causes a phototransistor’s beta to decrease when exposed to light**  
  - This statement is incorrect because the beta (current gain) of a phototransistor can actually increase when exposed to light, as the light generates additional charge carriers, enhancing its ability to conduct current. This is not the definition of the photovoltaic effect.

### Useful Formulas or Rules of Thumb:

- The efficiency of a solar cell can be estimated using the formula:

$$
\text{Efficiency} = \frac{P_{out}}{P_{in}} \times 100\%
$$

where:
- $P_{out}$ = electrical power output (in watts)
- $P_{in}$ = solar power input (in watts)

This formula helps in understanding how effectively a solar cell converts light energy into electrical energy. 

In summary, the photovoltaic effect is crucial for converting light into electrical energy, which is why option B is the correct answer.