Question

For a certain transistor, β = 50. Find the value of α.
1. 0.88
2. 0.98
3. 0.78
4. 0.68

Answer 1

Correct Answer - Option 2 : 0.98

Concept:

The common emitter current gain (β) is the ratio of the collector current (IC) to the base current (I­B)­.

\(\beta = \frac{{{I_C}}}{{{I_B}}}\)

The common base current gain (α) is the ratio of the collector current (IC) to the emitter current (I­E).

\(\alpha = \frac{{{I_C}}}{{{I_E}}}\)

The relationship between α and β is given by,

\(\alpha = \frac{\beta }{{\beta + 1}}\)

IC = α IE

\({I_C} = \frac{\beta }{{\beta + 1}}{I_E}\)

As β is very high, IC ≈ IE

Calculation:

Given that, β = 50

\(\alpha = \frac{{50}}{{50 + 1}} = 0.98\)