Question

What is the symbol of NOR gate?

Answer 1

The **NOR gate** is a fundamental digital logic gate that performs a combination of two basic logical operations: **NOT** and **OR**. The NOR gate produces an output that is the **inverse** (NOT) of the output of an **OR gate**. This means that the NOR gate outputs a **high** (1) only when all of its inputs are **low** (0); otherwise, it outputs **low** (0).

### Symbol of NOR Gate

The symbol of a NOR gate is a combination of the OR gate symbol and a **NOT** operation. Here's how it can be understood:

1. **OR Gate Symbol**: The OR gate symbol is a curved shape that looks like a "shield" or a "bow" (a curved line on the right side), and it has two or more inputs on the left side, depending on the number of variables it operates on.

2. **Inversion (NOT) Symbol**: The inversion of the OR gate is represented by a small circle (also called a **bubble**) at the output side. This circle indicates that the output is the negation of the OR operation.

   - **OR Gate Symbol**:  
     ```
      _______
     |       |
     |   ≥1   |
     |_______|
     ```
   - **NOR Gate Symbol**:  
     Add a small circle (inversion) to the output of the OR gate symbol. This is what makes it a **NOR gate**.
     ```
      _______
     |       |
     |   ≥1   |
     |_______|
         O
     ```

### Logical Operation of the NOR Gate

The behavior of the NOR gate is as follows:

- The output is **1** (high) only when **all** the inputs are **0** (low).
- In any other case, the output is **0** (low).

This can be summarized by the truth table for the NOR gate:

| Input A | Input B | Output (A NOR B) |
|---------|---------|------------------|
|    0    |    0    |        1         |
|    0    |    1    |        0         |
|    1    |    0    |        0         |
|    1    |    1    |        0         |

### Characteristics:
- The NOR gate is a **universal gate**, meaning you can use it to construct any other logic gate (AND, OR, NOT, etc.) by combining multiple NOR gates. This makes it very versatile in digital logic design.
- It is the **complement** of the OR gate, and as such, it's often used in digital circuits where negated outputs are needed.

### Summary:
- **Symbol**: The symbol for the NOR gate looks like an OR gate symbol with a small circle (inversion bubble) on the output side.
- **Truth Table**: It outputs **1** only when all inputs are **0**, otherwise, the output is **0**.