*Question G7B02:
Which of these classes of amplifiers has the highest efficiency?*  

*Correct Answer is  D: Class C*  

### AI Response: (may contain errors)  

Class C amplifiers have the highest efficiency among the given options. Here's why:

1. **Class C Amplifier Efficiency**:
   - Class C amplifiers are designed to conduct for less than 180 degrees of the input signal cycle. This means they are on for a very short portion of the cycle, which minimizes the time they spend in the active region where power is dissipated as heat.
   - The efficiency of a Class C amplifier can be very high, often exceeding 70% to 80%, because they are mostly off and only conduct during a small portion of the input cycle.

2. **Why Other Classes Are Less Efficient**:
   - **Class A**: 
     - Class A amplifiers conduct for the entire 360 degrees of the input cycle. They are always on, which means they dissipate a lot of power as heat, leading to low efficiency, typically around 20% to 30%.
   - **Class B**: 
     - Class B amplifiers conduct for 180 degrees of the input cycle. They are more efficient than Class A, with efficiencies around 50% to 60%, but still less efficient than Class C.
   - **Class AB**: 
     - Class AB amplifiers conduct for more than 180 degrees but less than 360 degrees. They are a compromise between Class A and Class B, offering better linearity than Class B and better efficiency than Class A, typically around 50% to 70%.

3. **Efficiency Formula**:
   - The efficiency ($\eta$) of an amplifier is given by:
     $$ \eta = \frac{P_{\text{out}}}{P_{\text{in}}} \times 100\% $$
   - Where $P_{\text{out}}$ is the output power and $P_{\text{in}}$ is the input power.

In summary, Class C amplifiers are the most efficient because they minimize the time spent conducting, reducing power loss as heat. This makes them ideal for applications where efficiency is more critical than linearity, such as RF transmission.