Open-circuit reflection at a transmission-line termination: Which statement correctly describes the voltage and current at the open end?

Introduction / Context:When a traveling wave reaches a mismatched termination, part or all of it reflects. An open circuit presents infinite impedance, resulting in a specific reflection behavior that sets the boundary conditions at the load.

Given Data / Assumptions:

• Lossless transmission line for clarity.
• Open-circuit load ZL → ∞.
• Incident voltage wave Vi with reflection coefficient Γ = +1 at the load.

Concept / Approach:

At an open, the reflected voltage is in phase with the incident voltage. Therefore, at the very end of the line V_total = Vi + Vr = 2Vi. Current must be zero at the open because no conduction path exists: I_total = Ii + Ir = 0. This is the standard boundary condition used in standing-wave analysis.

Step-by-Step Solution:

Verification / Alternative check:

Smith chart analysis places the open at the rightmost point (Γ = +1) with voltage maxima and current minima at the load, matching the derived result.

Why Other Options Are Wrong:

• Current doubling or both doubling violate the open-circuit boundary condition.
• Zero voltage corresponds to a short circuit, not an open.
• Unchanged values ignore reflections entirely.

Common Pitfalls:

Mixing up the signs for current reflection and confusing open- versus short-circuit cases.

Final Answer:

The voltage at the termination is twice the incident voltage