Which material is a poor conductor?

• A. Copper
• B. Aluminium
• C. Wood
• D. Water

Answer: (C)

Electric current moves most easily through materials that have many mobile charge carriers. Metals like copper and aluminum have lots of free electrons that can flow readily, so they are excellent conductors. Wood, by contrast, is an insulating material. In dry wood there are few free charges to carry current, and its structure includes air gaps and tightly bound molecules that resist the movement of electrons. That’s why wood does not conduct electricity well. Water’s conductivity depends on impurities: pure water conducts poorly, but ordinary tap water contains ions that carry charge, so it can conduct better than dry wood. So among common materials, wood behaves as a poor conductor.