0620 · 9.2Uses of metals

Matching metal properties to uses

0:00An aircraft, an overhead electrical cable and a food container have very different jobs. Yet aluminium is useful in all three. Copper is also a metal, but it is especially useful for electrical wiring. By the end of this video, you will understand how each choice follows from the properties that the job requires. Choosing a metal starts with understanding what it must do. A cable must carry an electric current, while an aircraft needs materials that avoid unnecessary mass.

0:25For food containers, the material should not deteriorate during use. The useful connection is always between a particular property and a particular need. Density is mass per unit volume, so a lower density means less mass for the same volume. Electrical conductivity describes how well a material carries an electric current. A ductile material can be drawn into wires without breaking. Density is not simply another word for mass. A large aluminium object can have more mass than a small copper object.

0:53To compare their densities fairly, imagine blocks with exactly the same volume. The aluminium block has less mass because aluminium has a lower density than copper. This makes aluminium useful in the manufacture of aircraft. For a given volume of material, its low density keeps the mass relatively small. An aircraft must be lifted and moved through the air. Avoiding unnecessary mass makes that task easier, which explains why low density matters here.

1:19Notice that good electrical conductivity does not explain this particular use. Aluminium can conduct electricity, but that is not the property linked to manufacturing aircraft in this topic. A material may have several useful properties. Your explanation should select the one that answers the needs of the stated application. An overhead electrical cable has two needs at once. It must carry an electric current, and it must remain suspended between supports.

1:43Aluminium has good electrical conductivity, allowing it to carry current effectively. Its low density also reduces the mass of a given volume of cable. A lower mass means less weight for the supports to carry. That becomes important when a cable stretches over a long distance. Aluminium therefore combines an electrical advantage with a weight advantage. Neither property alone gives the complete explanation for its use in overhead electrical cables.

Aluminium containers and copper wiring

2:07A food container presents a different problem because it must remain intact during use. Corrosion is the deterioration of a metal through chemical reactions with its surroundings. Aluminium resists corrosion, so it is useful for food containers. This resistance helps prevent the material from being gradually damaged. Resistance to corrosion does not mean aluminium can never react. It means that the material resists this kind of deterioration under suitable conditions of use.

2:32The reason for aluminium’s protection is covered in the video on corrosion of metals. Here, connect corrosion resistance directly to the container’s durability. Copper is used in electrical wiring because it combines good electrical conductivity with ductility. Conductivity lets the finished wire carry an electric current effectively. Because copper is ductile, it can be drawn into a long, thin wire. These properties meet different needs, so both belong in the explanation.

2:58Do not confuse ductility with malleability. A malleable material can be hammered or pressed into shape, especially into sheets, whereas ductility is about drawing it into wires. When explaining copper wiring, name ductility because the required shape is a wire, rather than a sheet.

Explaining metal choices in exams

3:13Suppose you must explain why aluminium is suitable for an overhead electrical cable. First, identify the job rather than listing everything you know about the metal. The cable carries current while hanging between supports, so there are two separate requirements. Next, match each requirement to a property. Good electrical conductivity meets the need to carry current. Low density limits the mass, reducing the weight that the supports must carry. The final explanation links both properties to the application, rather than merely saying aluminium is useful.

3:43Several mistakes come from choosing a true property that does not explain the stated use. Saying aluminium conducts electricity does not explain why it is chosen for aircraft. Describing copper as strong does not replace conductivity and ductility for wiring. Saying aluminium is light is also less precise than stating that it has low density. An exam question might ask you to state the properties that make each metal suitable for these uses.

4:06Aluminium is used in aircraft because of its low density. For overhead electrical cables, it has low density and good electrical conductivity. In food containers, aluminium is useful because it resists corrosion. Copper is used in electrical wiring because of its good electrical conductivity and ductility. If asked to explain a choice, make the link to the job clear. Low density reduces mass for a given volume, while conductivity allows current to flow.

4:31Ductility makes wire production possible, and corrosion resistance helps a container remain intact. Understanding those connections lets you explain all four uses without relying on an unrelated list of metal properties.