Which one of the following pairs of metals are very good conductors of heat?
- A.Silver and Copper
- B.Silver and Lead
- C.Copper and Mercury
- D.Lead and Mercury
Correct answer
Explanation
The correct answer is A, Silver and Copper. Silver and copper are the two best conductors of heat among metals.
Metals conduct heat because their free electrons carry energy quickly through the solid. Silver has the highest thermal conductivity of all metals, about 430 W/m·K, and copper comes close behind at about 400 W/m·K. Gold and aluminium follow. Copper is the practical choice for cooking-pot bottoms, radiators and heat exchangers because it is far cheaper than silver. Lead and mercury, by contrast, are poor conductors of heat for metals, with conductivities of only about 35 and 8 W/m·K.
B is wrong: lead conducts heat roughly ten times less well than silver.
C is wrong: mercury, a liquid metal, is one of the poorest metallic conductors of heat.
D is wrong: both lead and mercury are poor conductors of heat.
Exam tip: best conductors of heat and electricity, in order: silver, copper, gold, aluminium; lead and mercury are poor conductors.
Practice Questions
View allConsider the following animals :
1. Hedgehog
2. Marmot
3. Pangolin
To reduce the chance of being captured by predators, which of the above organisms rolls up/roll up and protects/protect its/their vulnerable parts?
- A.1 and 2
- B.2 only
- C.3 only
- D.1 and 3
Show answer
Hedgehogs and pangolins curl into a tight ball when threatened, covering the soft belly and face with spines or scales; marmots do not.
Read the full explanation →Which one of the following is used in preparing a natural mosquito repellent?
- A.Congress grass
- B.Elephant grass
- C.Lemongrass
- D.Nut grass
Show answer
Lemongrass and its close relative citronella grass yield aromatic oils that keep mosquitoes away, so they are the base of many natural repellents.
Read the full explanation →Which one of the following devices is non-ohmic ?
- A.Conducting copper coil
- B.Electric heating coil
- C.Semi conductor diode
- D.Rheostat
Show answer
A diode does not obey Ohm's law: the current through it is not proportional to the voltage across it. An ohmic conductor gives a straight-line graph of current against voltage, so its resistance stays constant at a fixed temperature.
Read the full explanation →What is the formula mass of anhydrous sodium carbonate? (Given that the atomic masses of sodium, carbon and oxygen are 23 u, 12 u and 16 u respectively)
- A.286 u
- B.106 u
- C.83 u
- D.53 u
Show answer
Anhydrous sodium carbonate is Na₂CO₃, and 2 × 23 + 12 + 3 × 16 = 106 u. Formula mass is the sum of the atomic masses of all the atoms in one formula unit of an ionic compound.
Read the full explanation →Which one of the following minerals is used as a fuel in nuclear power stations ?
- A.Bauxite
- B.Quartz
- C.Feldspar
- D.Pitchblende
Show answer
Pitchblende, or uraninite, is the chief ore of uranium, the fuel used in most nuclear power stations. Pitchblende is a heavy, black mineral made mostly of uranium oxide.
Read the full explanation →