A power amplifier delivers 25 W of ac power to a 4 Ω speaker load. If the dc input power is 40 W, what is the efficiency of this amplifier? 

Concept:

The efficiency of the power amplifier is given by;

\(η= \frac{P_{0}}{P_{i}}\times 100\)

Where;

η = Efficiency

P₀ = Output AC power

P_i = Input DC power

Calculation:

Given;

P0 = Output AC power =25 W

Pi = Input DC power = 40 W

Then;

\(η= \frac{P_{0}}{P_{i}}\times 100 = \frac{25}{40}\times 100 =62.5\,%\)