What is the function of a key (or switch) in an electric circuit ?

Answer

### Step-by-Step Solution:

1. **Understanding the Circuit**: An electric circuit consists of various components like resistors, batteries, and switches. The flow of electric current is essential for the functioning of these components.

2. **Role of a Key or Switch**: The primary function of a key (or switch) in an electric circuit is to control the flow of electric current. It acts as a gatekeeper for the circuit.

3. **Opening and Closing the Circuit**:
- **Closed Circuit**: When the switch is in the closed position, it completes the circuit, allowing current to flow through it. This is necessary for the operation of electrical devices.
- **Open Circuit**: When the switch is in the open position, it breaks the circuit, stopping the flow of current. This is useful for turning off devices when they are not needed.

4. **Maintaining Current Flow**: The switch helps in maintaining the current in the circuit. When current is required for a device to function, the switch is closed. Conversely, when the device is not in use, the switch is opened to prevent unnecessary current flow.

5. **Conclusion**: In summary, the key or switch is essential for controlling the operation of an electric circuit by allowing or stopping the flow of current as needed.