Cho mạch điện hình 1. Ucc = +12V; Rc = 2kΩ

To solve the given problem related to the transistor circuit, let's summarize the information and approach both parts (a and b):

### Given Data:
- \( U_{cc} = +12V \)
- \( R_c = 2kΩ \)
- \( R_1 = 150kΩ \)
- \( R_2 = 50kΩ \)
- \( R_e = 2kΩ \)
- \( \beta = 99 \)
- \( U_{BE} = 0.6V \)

### a. Determine the voltage and current across the transistor's terminals:
1. **Calculate the voltage at the base \( V_B \)**:

Use the voltage divider rule:
\[
V_B = U_{cc} \cdot \frac{R_2}{R_1 + R_2} = 12V \cdot \frac{50kΩ}{150kΩ + 50kΩ}
\]
\[
V_B = 12V \cdot \frac{50}{200} = 12V \cdot 0.25 = 3V
\]

2. **Calculate \( V_E \)**:
\[
V_E = V_B - V_{BE} = 3V - 0.6V = 2.4V
\]

3. **Calculate the emitter current \( I_E \)**:
Use Ohm's law for \( R_e \):
\[
I_E = \frac{V_E}{R_e} = \frac{2.4V}{2kΩ} = \frac{2.4}{2000} = 1.2mA
\]

4. **Calculate the base current \( I_B \)** using:
\[
I_E \approx I_C \quad (\text{since } I_E \approx I_C + I_B)
\]
\[
I_B = \frac{I_C}{\beta} = \frac{1.2mA}{99} \approx 0.0121mA
\]

5. **Calculate the collector current \( I_C \)**:
\[
I_C \approx I_E \approx 1.2mA
\]

### b. Functions of \( R_1 \) and \( R_2 \) in the Circuit:
1. **Function of \( R_1 \)**:
- \( R_1 \) determines the base biasing current. It ensures that the base voltage \( V_B \) is at an appropriate level to keep the transistor in the active region.

2. **Function of \( R_2 \)**:
- \( R_2 \) also plays a role in setting the base voltage, working with \( R_1 \) as part of a voltage divider to maintain stable operation of the transistor.

### Summary:
- The circuit configuration allows stable transistor operation by establishing a reliable bias point through \( R_1 \) and \( R_2 \).
- The currents and voltages across the transistor’s terminals can be calculated based on the resistances and given parameters.

If you have further specific questions or need more detailed calculations, feel free to ask!