Question

An npn transistor operates as a common emitter amplifier, with a power gain of 60 dB. The input circuit resistance is 100Ω and the output load resistance is 10 kΩ. The common emitter current gain β is ______.

Options

• 10²

• 60

• 6 × 10²

• 10⁴

Answer 1

An npn transistor operates as a common emitter amplifier, with a power gain of 60 dB. The input circuit resistance is 100Ω and the output load resistance is 10 kΩ. The common emitter current gain β is 10².

Explanation:

Power gain = 60 = 10log `("P"_0/"P"_"i")`

⇒ 6 = log`("P"_0/"I"_"b")`

⇒ `("P"_0/"I"_"b")` = 10⁶

= `beta^2("R"/"R"_"in")`

⇒ 10⁶ = `beta^2(10000/100)`    [as R_out = 10,000Ω R_in = 100Ω]

⇒ β = 100