Question

A transistor is connected in common-emitter (CE) configuration. The collector supply is 8V and the voltage drop across a resistor of 500 \( \Omega \) in the collector circuit is 0.6V. If the current gain factor \( \alpha \) is 0.96, find the base current.

• A. 25 \( \mu A \)
• B. 50 \( \mu A \)
• C. 20 \( \mu A \)
• D. 35 \( \mu A \)

Hint:

In a transistor’s common-emitter configuration, the current gain \( \alpha \) relates the collector and emitter currents. To find the base current, subtract the collector current from the emitter current.

Answer 1

The Correct Option is B

Step 1: Given: - Collector supply voltage \( V_C = 8 \, {V} \), - Voltage drop across the resistor \( V_R = 0.6 \, {V} \), - Resistor \( R_C = 500 \, \Omega \), - Current gain factor \( \alpha = 0.96 \). First, calculate the collector current using Ohm’s law: \[ I_C = \frac{V_R}{R_C} = \frac{0.6}{500} = 1.2 \times 10^{-3} \, {A} = 1.2 \, {mA} \] Step 2: The relationship between the collector current and emitter current is given by: \[ I_C = \alpha \cdot I_E \] where \( I_E \) is the emitter current. Rearranging the equation, we get: \[ I_E = \frac{I_C}{\alpha} = \frac{1.2 \, {mA}}{0.96} = 1.25 \, {mA} \] Step 3: The base current \( I_B \) is related to the emitter current by: \[ I_E = I_B + I_C \] Thus, the base current is: \[ I_B = I_E - I_C = 1.25 \, {mA} - 1.2 \, {mA} = 0.05 \, {mA} = 50 \, \mu {A} \] Thus, the base current is \( \boxed{50 \, \mu A} \).