Which of the following is NOT an example of an insulator?

Which of the following is NOT an example of an insulator?

• A. Copper
• B. Glass
• C. Plastic
• D. Wood

Answer: (A)

Understanding how easily charges can move through a material is the key idea. Metals like copper have many free electrons that can move freely when a voltage is applied, so they conduct electricity very well. That makes copper a good conductor, not an insulator, which is why it’s the correct choice for “not an insulator.” The other materials—glass, plastic, and dry wood—hold onto their electrons tightly and have few free charge carriers, so they resist current flow and are insulators. (Note that wood can conduct if it’s wet, but in dry form it acts as an insulator.)

Understanding how easily charges can move through a material is the key idea. Metals like copper have many free electrons that can move freely when a voltage is applied, so they conduct electricity very well. That makes copper a good conductor, not an insulator, which is why it’s the correct choice for “not an insulator.” The other materials—glass, plastic, and dry wood—hold onto their electrons tightly and have few free charge carriers, so they resist current flow and are insulators. (Note that wood can conduct if it’s wet, but in dry form it acts as an insulator.)