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The correct relation for α, β for a transistor

Asked in CBSE AIPMT 2000 · Transistor currents and current gain

• (1) β=(1-α)/α
• (2) β=α/(1-α)
• (3) α=(β-1)/β
• (4) αβ=1

Step-by-step solution

Why the other options are wrong

• (1) comes from this is the reciprocal of the right relation; it would make β less than 1 for any sensible α, when β is typically in the tens or hundreds.
• (3) α=(β-1)/β is close to but not the correct inversion, which is α=β/(1+β).
• (4) αβ=1 would force α to be tiny whenever β is large, but α is always just under 1.

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