*Question E5B12:
What is admittance?*  

*Correct Answer is  A: The inverse of impedance*  

### AI Response: (may contain errors)  

Admittance is a key concept in electrical engineering and is defined as the measure of how easily a circuit allows current to flow when a voltage is applied. It is the inverse of impedance.

### Correct Answer: A - The inverse of impedance

- **Explanation**: 
  Admittance ($Y$) is defined mathematically as:
  $$Y = \frac{1}{Z}$$
  where:
  - $Y$ = admittance in siemens (S)
  - $Z$ = impedance in ohms (Ω)

  This means that if you know the impedance of a circuit, you can find the admittance by taking its reciprocal. Admittance is composed of two components: conductance (real part) and susceptance (imaginary part).

### Why the Other Choices are Incorrect:

- **B: The term for the gain of a field effect transistor**  
  - **Explanation**: This choice refers to the concept of gain in transistors, which is not related to admittance. Gain is a measure of how much a transistor amplifies a signal, while admittance deals with the flow of current in response to voltage.

- **C: The inverse of reactance**  
  - **Explanation**: Reactance is a component of impedance that accounts for the opposition to current flow due to capacitance and inductance. While admittance is related to reactance, it is not simply the inverse of reactance. Instead, it is the inverse of the total impedance, which includes both resistance and reactance.

- **D: The term for the on-impedance of a field effect transistor**  
  - **Explanation**: On-impedance refers to the resistance of a transistor when it is in the "on" state, which is a specific characteristic of the transistor itself. This is not related to the general concept of admittance.

### Summary:
- Admittance is the inverse of impedance, allowing us to understand how easily current flows in a circuit.
- Remember the formula: 
  $$Y = \frac{1}{Z}$$
- Understanding the distinction between admittance and other electrical parameters is crucial for the Extra Class exam.