Resistivity of alloys
Alloys resist more than the metals they are made from.
Mixing metals
Constantan is made by mixing two metals, copper and nickel. Copper and nickel are both good conductors of electricity.
How does the resistivity of the alloy constantan compare with that of copper and nickel?
What this lesson covers
The idea
An alloy generally has a higher resistivity than its constituent metals and does not oxidise (burn) readily at high temperatures.
Mixing metals
Constantan is made by mixing two metals, copper and nickel. Copper and nickel are both good conductors of electricity.
How does the resistivity of the alloy constantan compare with that of copper and nickel?
- It is higher than both
- It is lower than both
- It is exactly halfway between them
Compare the bars
Open every tab. Orange bars are alloys.
Higher, and tough in the heat
In every picture the alloy had a longer bar than all its metals. Alloys also do not burn away in the heat, which is why they are used in heaters.
An alloy generally has a higher resistivity than its constituent metals and does not oxidise (burn) readily at high temperatures.
Notes
An alloy generally has a higher resistivity than its constituent metals and does not oxidise (burn) readily at high temperatures.
Check yourself
How does the resistivity of an alloy generally compare with that of the metals it is made from?
Why are alloys commonly used in electric irons and toasters?
According to the table of resistivities, which of these has the highest resistivity?
Nichrome is an alloy of nickel, chromium, manganese and iron. How is its resistivity compared with that of nickel?
- It is generally lower. Table 11.2 shows the resistivity of an alloy is generally higher than that of its constituent metals.
- It is generally higher — correct. Yes!
- It is always the same as the average of the metals. The resistivity of an alloy is generally higher than that of each of its constituent metals, not an average of them.
- They have the lowest resistivity of all materials. Alloys have a higher resistivity than their constituent metals, not a lower one.
- They are insulators. Alloys are good conductors with a low resistivity. The reason for their use in heaters is that they do not oxidise readily when hot.
- They do not oxidise (burn) readily at high temperatures — correct. Yes!
- Nichrome — correct. Yes!
- Copper. Copper has a resistivity of 1.62 × 10⁻⁸ Ω m, which is far less than nichrome's 100 × 10⁻⁶ Ω m.
- Iron. Iron has a resistivity of 10.0 × 10⁻⁸ Ω m, which is far less than nichrome's 100 × 10⁻⁶ Ω m.
- It is lower. An alloy generally has a higher resistivity than its constituent metals, and nichrome's is far higher than nickel's.
- It is higher — correct. Yes!
- It is the same. Nichrome's resistivity, 100 × 10⁻⁶ Ω m, is far higher than nickel's, 6.84 × 10⁻⁸ Ω m.