Set up the circuit in Figure 1. For the variable load resistor RL use a decade resistor box. Measure VL and calculate the power absorbed in R L, for a variety of values of resistance from RS/10 to 10RS. Plot the values of power absorbed vs. the load resistance RL. Find the value of RL which corresponds to a maximum on the graph. This should be the same value as RS. Is it? Comment. Comment also on the accuracy of this technique as a way of determining the value which maximizes the power transfer. Comment on the deviation from maximum which occurs when the load resistor deviates from the optimum value by 50 percent.
Figure 1.
A much more accurate way to determine the value of RL which maximizes power transfer is to make use of the Thevenin equivalent of the network in question. If the network is represented by its Thevenin equivalent (VOC and RTH in series) then when RL = RTH, the voltage across the RLwill be VOC/2. Thus the Thevenin equivalent resistance of any linear network can be determined by (1) measuring VOC, and (2) attaching an RL and changing it until the load voltage is VOC/2. This value maximizes the power transfer. Use this technique on the circuit above.
This technique also works if the sources in the network are sinusoidal, the difference being that RMS measurements are made rather than DC measurements. Adjust the function generator for zero DC offset and a frequency of 1 KHz. Then using the method of the previous paragraph, determine the RTH of the function generator (which, although shown as an ideal source in the circuit, actually has a nonzero internal resistance), and using the less accurate graphical method find the value of RL which maximizes the power transfer from the generator to its load.
Set up the circuit in Figure 2. Take enough readings of VS and VO to make an accurate graph of VO (vertically) on the graph vs. VS (horizontally). A smart way to do this is to use the scope in the "X-Y" mode, using VS as the X (CH1) input and VO as the Y (CH2) input, with the signal generator, running as a triangle generator, attached to the input terminals. Record the graph and comment on the linearity of the input/output relationship.
Figure 2.
Set up the linear circuit Figure 2, using the dual DC source. Set VS1 = 5 Volts and VS2 = 0 Volts, and record V4 and I1. Then set VS1 = 0 Volts and VS2 = 4 Volts, and record V4 and I1 again. Finally set VS1 = 5 and VS2 = 4 and record V4 and I1 once more. Comment on the relationship between the sets of readings.
Figure 3.