*Question E6C08:
In Figure E6-3, which is the schematic symbol for a NAND gate?*  

*Correct Answer is  B: 2*  

### AI Response: (may contain errors)  

In digital electronics, a NAND gate is a fundamental building block that performs a specific logical operation. 

1. **Correct Answer Explanation (Choice B: 2)**:
   - The NAND gate outputs a low signal (0) only when all its inputs are high (1). In schematic diagrams, the symbol for a NAND gate typically consists of an AND gate symbol with a small circle (representing NOT) at the output. This is why choice 2 is the correct representation of a NAND gate.

2. **Incorrect Choices Explanation**:
   - **Choice A: 1** - This symbol likely represents an AND gate, which outputs high only when all inputs are high, without the NOT operation.
   - **Choice C: 3** - This symbol may represent a NOR gate, which outputs high only when all inputs are low, again without the NOT operation at the output.
   - **Choice D: 4** - This symbol could represent an OR gate, which outputs high when at least one input is high, without the NOT operation.

3. **Useful Rules of Thumb**:
   - Remember that NAND gates are universal gates, meaning you can create any other gate (AND, OR, NOT) using just NAND gates.
   - The output of a NAND gate can be expressed as:
     $$ 
     Y = \overline{A \cdot B} 
     $$
   where $Y$ is the output, and $A$ and $B$ are the inputs. The overline indicates the NOT operation.

Understanding these symbols and their functions is crucial for interpreting circuit diagrams and for the Extra Class exam.