*Question E6A06:
What is the beta of a bipolar junction transistor?*  

*Correct Answer is  B: The change in collector current with respect to the change in base current*  

### AI Response: (may contain errors)  

The beta ($\beta$) of a bipolar junction transistor (BJT) is a key parameter that describes its current gain. 

### Correct Answer Explanation:
- **Correct Answer: B: The change in collector current with respect to the change in base current.**
  
  The beta ($\beta$) is defined as the ratio of the collector current ($I_C$) to the base current ($I_B$):
  
  $$
  \beta = \frac{I_C}{I_B}
  $$
  
  This means that for a small change in base current, the change in collector current is proportional to the beta value. A higher beta indicates that a small base current can control a much larger collector current, which is essential for amplification in BJTs.

### Incorrect Answer Explanations:
- **A: The frequency at which the current gain is reduced to 0.707.**
  
  This describes the cutoff frequency or the -3 dB point of a transistor's frequency response, not the beta. Beta is a static parameter related to current gain, not frequency.

- **C: The breakdown voltage of the base-to-collector junction.**
  
  This refers to the maximum reverse voltage that can be applied to the base-collector junction before breakdown occurs. It is a voltage specification, not related to the current gain of the transistor.

- **D: The switching speed.**
  
  This refers to how quickly a transistor can turn on and off, which is influenced by various factors including capacitance and resistance in the circuit. It is not defined as beta.

### Summary:
- Beta ($\beta$) is crucial for understanding how BJTs amplify signals.
- Remember the formula for beta: 
  $$
  \beta = \frac{I_C}{I_B}
  $$
- Focus on the definitions and characteristics of BJTs to differentiate between these concepts for the exam.