Which term describes materials that resist heat or electrical flow?

• A. Efficiency
• B. Perpetual Motion Machines
• C. Conductors
• D. Insulators

Answer: (D)

Materials that resist the transfer of heat or electricity are called insulators. An insulator has low thermal conductivity, so heat moves through it slowly, and high electrical resistance, so electric current doesn’t flow easily. That’s why materials like plastic, wood, rubber, and air are good at keeping heat or electricity from passing where you don’t want it to. This idea isn’t about how efficiently a device uses energy—that's something else—it's about how resisting the flow of energy helps keep heat in or out and protects against unwanted electrical flow. Conductors, by contrast, readily allow electricity to pass, which is the opposite property. Perpetual Motion Machines are not a property of materials.