EPE301C Course 1 Practice Test

The main idea is how to get the most power into a load from a fixed source using a Thevenin view. Replace the source and its internal resistance with a voltage V_th in series with R_th feeding the load R_L. The power in the load is P_L = V_th^2 × R_L / (R_th + R_L)^2. This expression is maximized when R_L equals R_th. The intuition is that with equal resistances, half of the voltage drops across the load and half across the internal resistance, giving the largest possible current through the load for a given V_th. In that case, the load receives V_th/2, the current is V_th/(2 R_th), and the power is V_th^2/(4 R_th).

Keep in mind: this result is for purely resistive loads. If the circuit has reactance, you generally need complex conjugate matching between impedances, not just equal resistances, to maximize real power transfer. The other scenarios—having the load much larger than R_th or the source with zero internal resistance—do not maximize the power delivered to the load in the general resistive Thevenin context.