Can we use a U-shaped permanent magnet in making an electric bell ?

Answer

To determine whether a U-shaped permanent magnet can be used in making an electric bell, we need to analyze how an electric bell operates and the role of the magnet involved.

### Step-by-Step Solution:

1. **Understanding the Components of an Electric Bell**:
- An electric bell consists of a battery, a switch, an electromagnet, a hammer, a gong, and a metal armature. The electromagnet is crucial for the operation of the bell.

2. **How the Electric Bell Works**:
- When the switch is closed, the electric circuit is completed, allowing current to flow through the electromagnet. This creates a magnetic field, causing the electromagnet to attract the metal armature.

3. **Action of the Hammer**:
- As the armature is attracted to the electromagnet, it moves towards the magnet and causes the hammer to strike the gong, producing sound.

4. **Breaking the Circuit**:
- When the armature moves towards the electromagnet, it breaks the circuit connection, stopping the current flow. This causes the electromagnet to lose its magnetism.

5. **Return of the Armature**:
- Once the current stops, the armature returns to its initial position, re-establishing the circuit. This allows the process to repeat, producing a continuous ringing sound.

6. **Using a Permanent Magnet**:
- If a U-shaped permanent magnet is used instead of an electromagnet, it will initially attract the armature and cause the hammer to strike the gong. However, since the permanent magnet does not lose its magnetism, the armature will remain attracted to the magnet.

7. **Consequences of Using a Permanent Magnet**:
- The armature will not return to its initial position because it is held by the permanent magnet. This means the circuit will remain broken, preventing the electric current from flowing again. As a result, the ringing sound will only occur once.

8. **Conclusion**:
- Therefore, while a U-shaped permanent magnet can cause the hammer to strike the gong initially, it cannot be used effectively in an electric bell because it does not allow the mechanism to reset and repeat the ringing process.

### Final Answer:
No, we cannot use a U-shaped permanent magnet in making an electric bell because it will not allow the armature to return to its initial position, preventing the electric bell from ringing repeatedly.