Problem 7.1   Source:   Problem elaborated by the author of the site.

Calculate the eletric power dissipated by the load R_L, in the circuit shown in Figure 07-01.1, when it assumes the following values: 1, 5, 10, 15, 25, 50 and 60 ohms, and tell what value of R_L dissipates the greatest eletric power.

Solution of the Problem 7.1

Let us through this problem show how the power dissipated by the load varies for different values of R_L. We will make a table for better understanding. The steps for mounting the table are determine the current I when R_L assumes the value 1 ohm and then calculate for subsequent values. So let's go solve for the value of 1 ohm and then repeat the same steps for the other values of R_L.

Now that we have the electric current flowing through R_L just apply the equation that calculates the power, or:

Doing similarly for the other R _L values, we can assemble the table as shown below.

In the table above, note the highlighted yellow line, which shows the conditions for maximum power dissipated in the load. In the Figure 07-01.2 appears the power graph according to the values of R_L (varying of 0 a 60 ohms).

Note that the peak of power dissipated by the load occurs exactly when the value of R_L is equal to the value of R₁. Therefore, we prove the validity of the maximum power transfer theorem .