Question

In a common emitter transistor circuit, if the emitter current is changed by 4 mA, the collector current changes by 3.5 mA, then the current gain is

• A. \(0.875\)
• B. \(3.5\)
• C. \(7\)
• D. \(0.5\)

Hint:

In a common emitter transistor circuit, the current gain (\(\beta\)) is given by: \[ \beta = \frac{\Delta I_C}{\Delta I_B} \] where \( I_B = I_E - I_C \). Always use this formula when dealing with transistor current gain calculations.

Answer 1

The Correct Option is C

Step 1: Understanding Current Gain in a Transistor The current gain (\(\beta\)) in a common emitter transistor circuit is defined as: \[ \beta = \frac{\Delta I_C}{\Delta I_B} \] where:
- \( \Delta I_C = 3.5 \) mA (change in collector current),
- \( \Delta I_E = 4 \) mA (change in emitter current),
- The relation between emitter, base, and collector currents is: \[ I_E = I_B + I_C \] Thus, the base current change is: \[ \Delta I_B = \Delta I_E - \Delta I_C \] Step 2: Calculating Base Current Change \[ \Delta I_B = 4 - 3.5 = 0.5 \, \text{mA} \] Step 3: Calculating Current Gain \[ \beta = \frac{3.5}{0.5} = 7 \] Thus, the correct answer is \( \mathbf{(3)} \ 7 \).