Correct Option
(c) A fuse is an essential safety device in electrical circuits, designed to protect appliances and prevent fire hazards caused by excessive current. It consists of a thin metallic wire, typically an alloy of tin and lead, which is specifically chosen for its low melting point. When the current flowing through the circuit exceeds a predetermined safe limit, the fuse wire heats up significantly due to the Joule heating effect. This rise in temperature causes the low-melting-point wire to melt and break the circuit, thereby interrupting the flow of excessive current and safeguarding the connected electrical system.
Incorrect Options:
(a) A fuse is always connected in series with the live wire of the electrical circuit, not in parallel. This series connection ensures that when the fuse wire melts due to an overcurrent, it completely breaks the circuit, stopping the flow of electricity to the protected appliance or section of the circuit.
(b) Fuses are generally made from alloys of metals like tin and lead, which possess a low melting point and suitable resistance characteristics. Silver alloys are not commonly used for fuses primarily due to their high cost, despite their excellent electrical conductivity. The objective is to have a material that melts reliably at a specific current, not necessarily the best conductor.
(d) A fuse must have a low electrical resistance to allow the normal operating current to pass through it without significant voltage drop or power loss. If a fuse had very high resistance, it would generate considerable heat and dissipate energy even under normal operating conditions, leading to inefficiency and potential premature melting. The critical characteristic is a low melting point combined with a resistance that causes it to heat up and melt only when the current exceeds the safe limit.