Question

A transistor is used in an amplifier circuit in common emitter mode. If the base current changes by 100µA, it brings a change of 10 mA in collector current. If the load resistance is 2kΩ and input resistance is 1kΩ, the value of power gain is x × 104 . The value of x is ______.

Options

• 2

• 4

• 5

• 3

Answer 1

A transistor is used in an amplifier circuit in common emitter mode. If the base current changes by 100µA, it brings a change of 10 mA in collector current. If the load resistance is 2kΩ and input resistance is 1kΩ, the value of power gain is x × 104 . The value of x is 2.

Explanation:

Power gain is defined as the ratio of output power to the input power.

Power gain = `"Output power"/"Input power"`

= `("I"_"output"^2xx"R"_"output")/("I"_"input"^2 xx "R"_"input")`

`(Deltai_"c")/(Deltai_"b") = "I"_"output"/"I"_"input"` β = current gain in common emitter mode

β = `(10^-2"A")/(10^-4"A") = 100`

∴ Power gain = (β)² × `"R"_"out"/"R"_"in"`

= `10^4xx (2xx10^3)/(1xx10^3) = 2xx 10^4`

Thus, value of x = 2