Given below are two statements, one is labelled as Assertion (A) and the other as Reason (R).
Assertion (A) : Generally an alloy of lead and tin is used as a material of the fuse wire.
Reason (R) : Al

Question

Given below are two statements, one is labelled as Assertion (A) and the other as Reason (R).
Assertion (A) : Generally an alloy of lead and tin is used as a material of the fuse wire.
Reason (R) : Alloy of lead and tin has a higher melting point than copper and aluminium.
Select the correct answer from the code given below :
Code :

UnlockIAS · Accepted Answer

Correct — B, (A) is true, but (R) is false. The Assertion is the standard textbook statement and it is correct: the wire in an ordinary rewirable fuse is an alloy of lead and tin. The Reason states the physics backwards. A lead-tin alloy melts at a very LOW temperature, not a high one — tin melts at about 232 degrees Celsius, lead at about 328, and their common alloys somewhere around 180 to 250 degrees. Copper melts at about 1,085 degrees Celsius and aluminium at about 660. So the fuse alloy melts far below copper and aluminium, not above them. That low melting point is the whole reason the alloy is chosen: the fuse is meant to be the deliberate weak link in the circuit, the one piece that gives way first when the current rises above the rated value, so that the copper or aluminium house wiring never gets hot enough to be damaged. Since (A) stands and (R) falls, the code is (b).

Why the other options are wrong — (a) This requires (R) to be true, and it is not. The claim that a lead-tin alloy melts at a higher temperature than copper and aluminium is factually wrong by roughly 800 degrees Celsius in the case of copper. A statement cannot be a non-explanatory truth when it is not a truth at all.  (c) This inverts the position exactly. The Assertion is the true half — lead-tin alloy really is the usual fuse-wire material — and the Reason is the false half. Anyone marking this option has read the two statements the wrong way round.  (d) The most seductive option, because a single word makes the difference. Had (R) read 'a LOWER melting point than copper and aluminium', it would have been both true and the correct explanation of (A), and (d) would have been the answer. As printed, (R) says 'higher', which reverses the property that makes the alloy usable, so (d) fails on the truth of (R) before the question of explanation even arises.

Concept: A fuse is a safety device deliberately built to be the weakest point of a circuit. It is a short, thin piece of wire connected in series in the live line, made of a metal or alloy chosen so that it melts at a low temperature. When current flows, heat is generated according to Joule's law, H = I squared times R times t, so the heating rises with the square of the current. If a short circuit or an overload pushes the current past the fuse's rated value, the thin low-melting element reaches its melting point long before the thick copper or aluminium conductors of the installation do; the fuse melts, the circuit is broken, and the wiring and appliances are saved. Lead-tin alloy suits the job because it combines a low melting point with an appreciable resistivity in a wire thin enough to heat quickly.

State PCS 2025 Q104 — Science & Technology PYQ with Answer

State PCS 2025 Q104 — Science & Technology PYQ with Answer