What are the constituents of alloy solder?
- (a)Pb and Zn
- (b)Pb and Sn
- (c)Pb and Si
- (d)Pb and Co
Correct — B, Pb and Sn. Solder is an alloy of lead and tin with a low melting point, and it is used for joining electrical wires together — a description the school text gives in one sentence. Its usefulness comes from that low melting point: a tin-lead mixture near the eutectic composition, about sixty per cent tin to forty per cent lead, melts around 183 °C, well below either pure metal and far below the copper it is used to join, so the joint can be made without damaging the wires or the components. Lead brings a low melting point and good wetting; tin does the actual bonding to the copper surface. None of the other three pairs has that property. Modern electronics has largely moved on from this formula, since restrictions on hazardous substances have pushed manufacturers towards lead-free solders based on tin with silver and copper, but the tin-lead alloy is still what the syllabus means by solder.
- (a)Pb and Zn — Lead and zinc are mined together and separated in the same smelters, which makes the pair sound plausible, but they are not the constituents of solder. Zinc alloyed with copper gives brass instead.
- (c)Pb and Si — Silicon is a metalloid used in semiconductors, not an alloying partner for lead in a low-melting joining alloy.
- (d)Pb and Co — Cobalt is a high-melting metal used in magnets, superalloys and battery cathodes. Adding it would raise the melting point rather than lower it.
An alloy is a homogeneous mixture of a metal with one or more other metals or non-metals, made to obtain properties the pure metal lacks. Alloys generally have lower electrical conductivity and a lower melting point than the parent metals, which is exactly why solder exists. The standard school set is worth holding together: brass is copper with zinc, bronze is copper with tin, solder is lead with tin, steel is iron with carbon, and an alloy containing mercury is called an amalgam.
The four options share lead and differ only in the partner, so the whole item rests on remembering one pairing. Two facts make it stick. First, solder has to melt below the metals it joins, and tin and lead are both low-melting metals — a combination of two high-melting metals could not do the job. Second, tin turns up twice in the school list, with copper in bronze and with lead in solder, which is a useful cross-check when the memory wavers. The property that matters here is one of the general rules about alloys: brass and bronze are poor conductors of electricity compared with the copper they are made from, and the same drop in conductivity applies to solder, which is why a soldered joint is a mechanical and electrical bridge rather than a superior conductor.
- Solder is an alloy of lead and tin, has a low melting point and is used for welding electrical wires together.
- A near-eutectic tin-lead solder melts at about 183 °C, below the melting point of either pure metal.
- Brass is an alloy of copper and zinc; bronze is an alloy of copper and tin; both conduct electricity less well than pure copper.
- An alloy in which one of the metals is mercury is called an amalgam.
- Restrictions on hazardous substances have pushed electronics manufacturing towards lead-free solders based on tin with silver and copper, though tin-lead solder remains the textbook example.
- Confusing bronze (copper with tin) with solder (lead with tin) because both contain tin.
- Assuming an alloy always conducts better than its parent metals; alloys usually conduct less well.
- Reading 'welding electrical wires' as arc welding; soldering works far below the melting point of the wires being joined.
As a name-the-constituents item, as a match list of alloys against their components or uses, or as a property question on why a low melting point matters.
Which are the materials generally employed as solder in soldering operation in electronics?
- (a) Iron and tin
- (b) Lead and tin
- (c) Aluminum and lead
- (d) Aluminum and iron
Answer(b) Lead and tin
The same fact asked by the Civil Services paper six years earlier, with the same answer and almost the same distractor logic — every wrong option pairs a high-melting metal that could not give a low-melting joining alloy.
Solder is an alloy of
- (a) Cu and Sn.
- (b) Fe and Zn.
- (c) Pb and Sn.
- (d) Ag and Zn.
Answer(c) Pb and Sn.
The identical question set six months earlier in the NDA paper. Its first option, copper with tin, is bronze — the mix-up this pairing invites most often.
- practice — not a real PYQ
Bronze is an alloy of
- (a)copper and zinc
- (b)copper and tin
- (c)lead and tin
- (d)iron and carbon
Answer(b) copper and tin — brass is the copper-zinc alloy, while lead with tin gives solder.
- practice — not a real PYQ
An alloy in which one of the constituent metals is mercury is known as
- (a)an amalgam
- (b)a solder
- (c)a bronze
- (d)a duralumin
Answer(a) an amalgam — the term applies to any alloy of mercury with another metal.