Question

The values of z12 and z22 for a T circuit having resistances 20 Ω each is _____________

(a) 40, 20

(b) 40, 60

(c) 20, 40

(d) 40, 40

Answer 1

The correct choice is (c) 20, 40

To explain I would say: To find z12 and z22, we apply a voltage source V2 to the output port and leave the input port open.

Thus, z12 = \(\frac{V_1}{I_2}   = \frac{(20) I_2}{I_2}\)

= 20 Ω

Now, z22 is the input impedance at port 1.

So, z22 = \(\frac{V_2}{I_2}  = \frac{(20+20) I_2}{I_2}\) = 40 Ω.