In household electrical circuits, fuse wire is commonly made of which material so that it melts quickly and safely when the current exceeds a safe level?

Introduction / Context:
A fuse is an important safety device used in household and industrial electrical circuits to protect appliances and wiring from damage due to excessive current. The fuse wire is designed to melt quickly when too much current flows, breaking the circuit and preventing overheating or fire. This question asks which material is commonly used to make fuse wire so that it has the correct melting characteristics for this protective function. Understanding why a specific alloy is chosen helps reinforce basic concepts in electricity and materials science.

Given Data / Assumptions:
- A fuse wire must have a low melting point compared to normal conducting wires in the circuit.
- It should also have reasonably high electrical resistance compared to copper so it heats up faster under excess current.
- The material should be predictable and reliable in its behavior when current rises above the rated value.
- Common conductors like copper or aluminium are typically used for regular wiring, not as fuse elements in simple low voltage fuses.

Concept / Approach:
Fuse wire works on the heating effect of electric current. According to the basic idea, heat produced in a conductor is proportional to I^2 * R * t, where I is current, R is resistance, and t is time. A fuse must heat up and melt quickly when current exceeds a safe limit. An alloy of tin and lead has a relatively low melting point and suitable resistance, making it ideal for this purpose. Pure copper or aluminium have much higher melting points and lower resistance, so they are not suitable as simple fuse elements. Therefore, the correct option will be the one that mentions the tin lead alloy.

Step-by-Step Solution:
Step 1: Recall that a good fuse material should melt easily when current is high, which requires a low melting point. Step 2: Check option A, an alloy of tin and lead, which is known to have a low melting point and is commonly used in simple fuse wires. Step 3: Check option B, nickel, which has a relatively high melting point and is not widely used as fuse wire in household applications. Step 4: Check option C, copper, which is a very good conductor used for wiring but has too high a melting point for a simple fuse element. Step 5: Check option D, an alloy of nickel and lead, which is not standard fuse wire material and does not match common practice. Step 6: Check option E, pure aluminium wire, which again is more suited to conductors and not usually used as a low melting fuse wire. Step 7: Conclude that an alloy of tin and lead is the correct answer.

Verification / Alternative check:
To verify, think about the typical low cost cartridge or rewirable fuses used in many basic circuits. Textbooks and laboratory kits often mention that fuse elements are made of special alloys such as tin lead, sometimes with small additions of other metals, exactly because these alloys have predictable and relatively low melting points. Standard copper or aluminium wiring in the same circuit would not melt at those lower currents, proving that the fuse material must be different and more easily fusible than normal wiring.

Why Other Options Are Wrong:
Nickel has a high melting point and is not a standard choice for simple fuse wire in household circuits, so option B is not correct.
Copper is mainly used for conductors and power cables due to its low resistance and high melting point; these properties make it unsuitable for fuse wire, so option C is wrong.
An alloy of nickel and lead is not a commonly cited fuse material and does not have the widely used characteristics associated with fuse wire, so option D is incorrect.
Pure aluminium wire is used as a conductor in some overhead lines but again has a higher melting point and is not commonly used as a fuse element, which makes option E wrong.

Common Pitfalls:
A typical mistake is to assume that any good conductor used for wiring, such as copper or aluminium, can also serve as fuse wire. Students forget that the role of a fuse is to fail safely under excessive current, which requires a different set of properties from those used for ordinary conductors. Another pitfall is not paying attention to the word alloy and assuming that pure metals are always better choices. In reality, controlled alloys like tin lead are deliberately designed to achieve the correct melting point for safety devices.

Final Answer:
An alloy of tin and lead is commonly used to make fuse wire in household electrical circuits because it has a suitable low melting point and resistance that allow it to melt quickly and safely when the current becomes excessive.