Q1: Which of the following low melting alloy containing bismuth and lead is used for electric fuse ?

ANS:A - Wood's metal

Wood's metal is a eutectic alloy composed mainly of bismuth, lead, tin, and cadmium. Its low melting point and other properties make it useful for various applications, including the manufacturing of electric fuses.

1. Composition: Wood's metal typically consists of approximately 50% bismuth, 25% lead, 12.5% tin, and 12.5% cadmium. The exact composition may vary depending on the specific application requirements.
2. Low Melting Point: One of the most notable properties of Wood's metal is its low melting point, which is around 70 °C (158 °F). This characteristic makes it suitable for applications where a low melting point is desired, such as in electric fuses.
3. Fuse Applications: In electric fuses, Wood's metal is used as a fusible element. When the current flowing through the fuse exceeds the rated value, it generates heat. As the temperature rises, the Wood's metal within the fuse melts at its low melting point. This melting causes the circuit to break, interrupting the flow of electricity and protecting the electrical system from damage due to overcurrent conditions.
4. Non-Toxicity: Wood's metal is relatively non-toxic compared to other fusible alloys, making it suitable for applications where contact with humans or the environment is possible. However, appropriate safety measures should still be taken when handling molten metal or its fumes.
5. Other Uses: Aside from electric fuses, Wood's metal has other applications. It is used in soldering, casting of small parts, making metal-in-glass seals for electronics, and as a low-temperature casting material for prototyping and specialized manufacturing processes.

In summary, Wood's metal is a eutectic alloy known for its low melting point and is commonly used in electric fuses due to its ability to melt at relatively low temperatures when exposed to overcurrent conditions, thereby protecting electrical systems from damage.