*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 of a bipolar junction transistor (BJT), often denoted as $\beta$ or $h_{FE}$, is a key parameter that describes the transistor's current amplification capability.

### Correct Answer: B
- **The change in collector current with respect to the change in base current**:  
  The beta ($\beta$) of a BJT is defined as the ratio of the change in collector current ($\Delta I_C$) to the change in base current ($\Delta I_B$). Mathematically, it is expressed as:  
  $$\beta = \frac{\Delta I_C}{\Delta I_B}$$  
  This means that for a small change in the base current, the collector current changes by $\beta$ times that amount, indicating the transistor's ability to amplify current.

### Why Other Choices Are Incorrect:
- **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 frequency response, not the beta. It is related to the frequency response of the transistor, not its current gain in the DC or low-frequency region.

- **C: The breakdown voltage of the base-to-collector junction**:  
  This refers to the voltage at which the base-to-collector junction breaks down and conducts in reverse, which is a different parameter known as the breakdown voltage, not beta.

- **D: The switching speed**:  
  The switching speed of a transistor is related to how fast it can turn on and off, which involves parameters like rise time and fall time, not the current gain (beta).

Understanding beta is crucial for analyzing and designing circuits that use BJTs, as it directly affects how much a small input current can control a larger output current.