*Question T9B05:
What happens as the frequency of a signal in coaxial cable is increased?*  

*Correct Answer is  D: The loss increases*  

### AI Response: (may contain errors)  

As the frequency of a signal in coaxial cable is increased, the loss increases. Let's break down why this is the correct answer and why the other choices are incorrect.

### Correct Answer: D - The loss increases

- **Explanation**: 
  - Coaxial cables have inherent resistive losses due to the resistance of the conductors and dielectric losses in the insulating material. As frequency increases, the skin effect causes the current to flow primarily on the surface of the conductor, which increases the effective resistance. Additionally, dielectric losses in the insulation material also tend to increase with frequency. Therefore, overall losses in the cable increase as the frequency rises.

### Why the Other Choices are Incorrect:

- **A: The characteristic impedance decreases**  
  - **Explanation**: The characteristic impedance ($Z_0$) of a coaxial cable is determined by its physical dimensions and the dielectric material used. It is given by the formula:
    $$Z_0 = \frac{1}{2\pi} \sqrt{\frac{L}{C}}$$
    where $L$ is the inductance per unit length and $C$ is the capacitance per unit length. Neither $L$ nor $C$ changes with frequency in a way that would decrease $Z_0$. Thus, this statement is incorrect.

- **B: The loss decreases**  
  - **Explanation**: As explained earlier, losses in coaxial cables actually increase with frequency due to both resistive and dielectric losses. Therefore, this statement is incorrect.

- **C: The characteristic impedance increases**  
  - **Explanation**: Similar to choice A, the characteristic impedance is not frequency-dependent in a way that would cause it to increase. It remains constant for a given coaxial cable design. Thus, this statement is also incorrect.

### Summary

- As frequency increases, the loss in coaxial cable increases due to:
  - Increased resistive losses from the skin effect.
  - Increased dielectric losses in the insulation.
  
Understanding these principles will help you answer similar questions on the Extra Class exam effectively.