In household electrical wiring, a fuse is used in the main supply as a safety device. Which of the following statements correctly describes a good fuse wire?

Introduction / Context:
This question tests basic knowledge of safety devices in electrical circuits. A fuse is a simple but vital protection component in domestic and industrial installations. Its purpose is to break the circuit automatically when current exceeds a safe limit, preventing overheating and possible fire or equipment damage. To play this sacrificial protective role, a fuse wire must be chosen with specific material properties. Understanding these properties is important for safely designing or using electrical systems.

Given Data / Assumptions:

• A fuse is connected in the mains supply of a circuit as a safety device.
• The options describe how it is connected, what it is made of, its melting point and its resistance.
• We must identify the correct essential property of a fuse wire.
• We assume a standard domestic alternating current supply and conventional fuse design.

Concept / Approach:
A fuse wire is designed to melt and break the circuit when the current exceeds a predetermined safe value. This means that the fuse should heat up quickly when current is too high. For this to happen reliably, the material should have a low melting point and a suitable resistance so that excess current causes sufficient heating. It is always connected in series with the load, not in parallel. While expensive metals like silver may be used in special fuses, common domestic fuses use inexpensive alloys like tin and lead. Very high resistance would cause significant energy loss even at normal currents, which is undesirable. Therefore, the key correct statement is that a fuse wire must have a low melting point.

Step-by-Step Solution:
Step 1: Recall that the function of a fuse is to melt and open the circuit when current becomes abnormally high. Step 2: For the fuse to melt quickly during overload, the material should have a low melting point and appropriate cross sectional area so that heating is concentrated in the fuse. Step 3: The fuse is always placed in series with the live supply line so that all current flows through it; if it were in parallel, current could bypass it and it would not provide protection. Step 4: The material used for domestic fuses is usually an inexpensive alloy with a definite and relatively low melting point, not costly metals like silver in ordinary installations. Step 5: The resistance of the fuse should be low under normal current so that it does not waste power significantly; extremely high resistance is not desired. Step 6: Conclude that the statement about having a low melting point is the correct one among the options.

Verification / Alternative check:
One can verify this by considering what happens during an overload due to a short circuit or too many appliances. The current suddenly increases, causing rapid heating in the fuse wire. Because its melting point is low compared to other conductors, it melts first and breaks the circuit before the main wiring overheats. If the fuse wire had a high melting point, other parts of the circuit might get damaged before the fuse reacts. This practical insight confirms that low melting point is an essential property of fuse wires.

Why Other Options Are Wrong:
If the fuse were connected in parallel with the main switch, current could bypass it and the fuse would not effectively protect the circuit; correct installation is in series. Common domestic fuse wires are not made mainly from silver alloys; they use cheaper alloys like tin lead combinations tuned to specific melting points. A very high resistance fuse would cause unacceptable voltage drop and power loss even at normal currents, which is not desirable in household circuits.

Common Pitfalls:
Students sometimes confuse properties needed for efficient conductors with those needed for fuse materials and may think that high melting point or very low resistance is always best. It is important to remember that a fuse is intentionally designed to fail safely and quickly under overload, so a controlled low melting point is crucial. Another common error is misunderstanding series and parallel connections. For exam preparation, always associate fuses with series connection and low melting point materials.

Final Answer:
The correct statement about a good fuse wire is that it must have a low melting point so that it melts and breaks the circuit when the current becomes too high.