Conduction of Heat and Electricity

Class 7 Science · Chapter 4: The World of Metals and Non-metals · NCERT Curiosity section 4.1.4–4.1.5

Learn

Ishaan puts a steel spoon and a wooden spoon of the same size into a glass of hot water. After a few minutes, the top of the steel spoon is hot, while the wooden one is barely warm. Heat travels along the metal: this is conduction, and materials that pass heat on are conductors.

Metals are good conductors of heat; wood and plastic are poor conductors. That is why cooking pans are made of metal but have wooden or plastic handles: the pan heats the food while the handle stays cool enough to hold. We explore heat flow more in the chapter on heat transfer.

With the tester circuit from the electricity chapter, aluminium foil, an iron nail and copper wire light the bulb; sulfur, coal, wood, stone, rubber and nylon do not. All the materials that conduct electricity are metals. Poor conductors keep us safe: screwdriver handles are plastic and electricians wear rubber gloves.

Summary of metals: generally hard, lustrous, malleable, ductile, sonorous, and good conductors of heat and electricity. Which metal for a pan to boil water? A good heat conductor that does not melt or burn, like copper, aluminium or iron, not sulfur, coal, plastic or wood.

Explore: conductor or not?

1. Test each object with the tester and sort it.

Remember

• Metals conduct heat and electricity well; non-metals like sulfur and coal do not.
• Poor conductors make handles, gloves and wire coverings for safety.

Quick check

Why do pans have wooden handles?

1. wood is a poor conductor of heat
2. wood conducts heat well
3. wood is a metal
4. wood is shiny

Think about it

Copper vessels are used to boil water. Is it because copper conducts electricity well?

Practice

Practise with fresh questions at three levels (easy, medium, hard), some answered hands-on, with hints and worked answers. Get 4 of your last 5 right to finish the topic.