Which statement best defines an insulator?

• A. The rate at which work is done.
• B. A material in which electrons are not able to move easily.
• C. The rate at which electrical charge passes a point.
• D. A material that allows electricity to flow through it easily.

Answer: (B)

An insulator is a material in which electrons are not able to move easily, so it resists the flow of electric current. Because the electrons are tightly bound and the energy required to free them into a conducting path is large, such materials have high resistivity and little current flows under normal voltages. This is why materials like rubber, plastic, and glass are used as insulators around wires. The other statements describe different electrical ideas: one is about power (the rate at which work is done), another is about current (the rate of charge flow), and a material that lets electricity flow easily is a conductor, not an insulator.