Topic: Electromagnetics
The outer conductor diameter and the inner conductor diameter dimensions of a coaxial cable are made twice to its original value. (Coaxial line is filled with dielectric material having dielectric constant $\epsilon_{r}=4.0,$). The correct statement is
- A. impedance remain same to it's original value
- B. impedance reduces to half of it's original value
- C. impedance increase and becomes twice of original value
- D. None of above
Answer: A. impedance remain same to it's original value
Explanation: $Z_{o}=\frac{138}{\sqrt{\epsilon_{r}}}ln\frac{D}{d}$, where, D = Diameter of outer conductor, d = Diameter of inner conductor. Now, when the outer conductor and inner conductor dimensions are doubled, the ratio $D/d$ remains same, so there is no change to the original value of impedance.