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e x a m p l e 2.33 v o l t a g e - c o n t r o l l e d r e s i s t o r Thus far we have dealt with resistors that have a fixed resistance. However, like dependent sources, we can also have resistors whose values depend on other parameters. As an example, Figure 2.71 depicts a voltage-controlled resistor whose resistance RX is a function of vI . Let us suppose we are interested in determining vO as a function of vI for RX = f (vI ) = Ro vI where Ro is some known constant. Let Ro = 5 k/V. First, R1 and R2 form a simple voltage divider, and since R1 = R2 , we have vI = V/2. Second, RL and RX also form a voltage divider. Therefore, vO = V =V =V =V =V = RX RL + RX Ro vI RL + Ro vI 5 k/vI 10 k + 5 k/vI vI 2 + vI V 2 2+ V2 4+V V 2 . Substituting V = 5 V, we find that vO = 25/9 V. R1 = 100 k Ω F I G U R E 2.71 Circuit with voltage-dependent resistor. V + 5 V - vI R2 = 100 k Ω 107a RL = 10 kΩ vO RX = f(vI)