A common emitter amplifier has a voltage gain of 50, an input impedance of `200 Omega` and an output impedance of `400 Omega`. Calculate the power gain of the amplifier.

Options

A. 500
B. 1000
C. 1250
D. 100

Answer

C

Explanation

AC power gain ` = ("Change in output power")/("Change in input power") `
` = ( Delta V_c xx Delta i_ c) /( Delta V_i xx Delta i_b) `
` = ((Delta V_ c)/( Delta V_i)) xx ( ( Delta i_c)/(Delta i_b)) `
` = A_V xx beta _(AC) `
where, ` A_V ` is voltage gain and ` (beta ) _ (AC)` is AC current gain.
Also, ` A_V = beta _(AC) xx ` resistance gain
` ( = (R_o)/(R_i)) `
Given, ` A _V = 50 , R_o = 200 Omega `,
` R_i = 100 Omega `
Hence, ` 50 = beta _ (AC) xx (200)/(100) `
` therefore beta _(AC) = 25 `
Now, AC power gain = ` A _V xx beta _ (AC ) `
` = 50 xx 25 `
` = 1250 `