A two-port network has Z11 = 20 Ω, Z22 = 10 Ω, Z12 = Z21 = 5 Ω. Then1.Network is reciprocal.2.Input impedance depends on load connected.3.Z-parameters are valid for open-circuit conditions.4.Z12 equals Z21 for symmetric networks only.Which of the above statements is/are correct?
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Z-parameters express two-port terminal voltages as linear combinations of port currents. Reciprocity requires Z12=Z21; symmetry additionally requires Z11=Z22. Key relation: V1=Z11I1+Z12I2; V2=Z21I1+Z22I2.
Exam focus: Reciprocal: Z12=Z21. Symmetric: Z11=Z22. Common trap: Do not confuse reciprocity with symmetry.
Formula / Key Relation
V1=Z11I1+Z12I2; V2=Z21I1+Z22I2.
Detailed Explanation
Correct Answer: C - 1, 2 and 3 only Quick Concept Explanation Z-parameters express two-port terminal voltages as linear combinations of port currents. Reciprocity requires Z12=Z21; symmetry additionally requires Z11=Z22. Key relation: V1=Z11I1+Z12I2; V2=Z21I1+Z22I2.Exam focus: Reciprocal: Z12=Z21. Symmetric: Z11=Z22. Common trap: Do not confuse reciprocity with symmetry. Statement-wise Verification Statement 1 - Correct.Network is reciprocal.V1=Z11I1+Z12I2; V2=Z21I1+Z22I2. Statement 2 - Correct.Input impedance depends on load connected.They are conveniently measured with open-circuit conditions because setting one port current to zero exposes the relevant impedance coefficient. Statement 3 - Correct.Z-parameters are valid for open-circuit conditions.Z-parameters express two-port terminal voltages as linear combinations of…
Correct Answer: C - 1, 2 and 3 only
Quick Concept Explanation
Z-parameters express two-port terminal voltages as linear combinations of port currents. Reciprocity requires Z12=Z21; symmetry additionally requires Z11=Z22. Key relation: V1=Z11I1+Z12I2; V2=Z21I1+Z22I2.
Exam focus: Reciprocal: Z12=Z21. Symmetric: Z11=Z22. Common trap: Do not confuse reciprocity with symmetry.
Statement-wise Verification
Statement 1 - Correct. Network is reciprocal. V1=Z11I1+Z12I2; V2=Z21I1+Z22I2.
Statement 2 - Correct. Input impedance depends on load connected. They are conveniently measured with open-circuit conditions because setting one port current to zero exposes the relevant impedance coefficient.
Statement 3 - Correct. Z-parameters are valid for open-circuit conditions. Z-parameters express two-port terminal voltages as linear combinations of port currents.
Statement 4 - Incorrect. Z12 equals Z21 for symmetric networks only. The correct principle is: Reciprocal: Z12=Z21. Symmetric: Z11=Z22.
Core Concept
Z-parameters express two-port terminal voltages as linear combinations of port currents. They are conveniently measured with open-circuit conditions because setting one port current to zero exposes the relevant impedance coefficient. Reciprocity requires Z12=Z21; symmetry additionally requires Z11=Z22.
Formula / Key Relationship
V1=Z11I1+Z12I2; V2=Z21I1+Z22I2.
Why the Other Options Are Wrong
Option A is incorrect because it omits correct statement(s) 1. Option B is incorrect because it includes incorrect statement(s) 4 and omits correct statement(s) 2, 3. Option D is incorrect because it includes incorrect statement(s) 4.
Exam Shortcut / Approach
Reciprocal: Z12=Z21. Symmetric: Z11=Z22.
Common Mistake
Do not confuse reciprocity with symmetry.
Quick Revision
Reciprocity and Loaded Input Impedance is linked with Z-Parameters, Two-Port Networks and Network Theory. Reciprocal: Z12=Z21. Symmetric: Z11=Z22.
Quick Trick
Reciprocal: Z12=Z21. Symmetric: Z11=Z22.
Why Other Options Are Wrong
Option A is incorrect because it omits correct statement(s) 1. Option B is incorrect because it includes incorrect statement(s) 4 and omits correct statement(s) 2, 3. Option D is incorrect because it includes incorrect statement(s) 4.
Common Mistake
Do not confuse reciprocity with symmetry.
Exam Tip
Reciprocal: Z12=Z21. Symmetric: Z11=Z22.
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