Which statement about 50 ohm coax is true?

• A. It can carry higher voltage than 75 ohm because it has lower impedance
• B. It has higher impedance than 75 ohm
• C. It always costs less than 75 ohm
• D. It is never used for power transmission

Answer: (A)

The important idea here is how impedance relates to voltage and power on a matched transmission line. For a line carrying a given RF power, the line voltage is linked by V_rms = sqrt(P × Z0). That means for the same power, a higher impedance (like 75 ohms) produces a higher voltage on the line than a lower impedance (like 50 ohms). Conversely, at the same line voltage, a 50-ohm line would deliver more power than a 75-ohm line because P = V^2 / Z0.

So the statement that a lower-impedance coax can carry higher voltage than a higher-impedance coax isn’t correct for the same transmitted power. The ability of a coax to carry voltage is mainly set by the dielectric and conductor geometry (dielectric breakdown, spacing), not simply its impedance. It’s also not guaranteed that 50-ohm coax costs less, and coax is indeed used for power transmission in RF systems.