Black Box
Given: An electrically active black box with two terminals produces a voltage of 80 V across a variable resistance resulting in a current of I A, as shown in the upper left figure. After changing the variable resistor, the same black box produces a voltage of 40 V across the resistance with a current of 2 A, as shown in the upper right figure.
Required: Calculate the value of a replacement load resistor, RL, that will draw the maximum power from the black box when it is placed across its terminals. Also, calculate the maximum amount of power that can be delivered to this resistor from the black box.
Solution:
RL =
U
Pmax
w