Who lets heat through?

The idea

Materials such as metals that let heat pass through them easily are good conductors of heat; materials such as glass, wood, clay and porcelain that resist its passage are poor conductors (insulators) of heat.

Pema asks a question

Pema watches her grandmother cook thukpa in a large metal pan. She asks, "Why are cooking utensils generally made of metals?"

What do you think is the reason?

• Metals let heat pass through them easily
• Metals are always the cheapest
• Metals never get hot

Heat one end of each

Tap Heat on each material. See how far the heat travels.

Good and poor

In the steel spoon and the copper rod the heat ran all the way along. In glass, wood, clay and porcelain it hardly moved.

Materials such as metals that let heat pass through them easily are good conductors of heat. Materials such as glass, wood, clay and porcelain that resist its passage are poor conductors (insulators) of heat.

• Material | Kind of conductor
• Metals (steel, copper) | Good conductor
• Glass | Poor conductor (insulator)
• Wood | Poor conductor (insulator)
• Clay, porcelain | Poor conductor (insulator)

Notes

Materials such as metals that let heat pass through them easily are good conductors of heat; materials such as glass, wood, clay and porcelain that resist its passage are poor conductors (insulators) of heat.

Check yourself

Why do we use metal utensils for cooking?

Which of these is a poor conductor of heat?

Tea or coffee stays hot longer in a clay or porcelain cup. Why?

Another name for a poor conductor of heat is …

• Metals are poor conductors, so they stay cool. Metals are good conductors. That is why heat from the flame reaches the food.
• Metals cannot be heated. Metals heat up easily because they let heat pass through.
• Metals are good conductors, so heat passes through them easily — correct. Yes!
• Wood — correct. Yes!
• Steel. Steel is a metal, and metals are good conductors.
• Copper. Copper is a metal, and metals are good conductors.
• Clay and porcelain are good conductors. Good conductors would let the heat go out quickly. Clay and porcelain resist the passage of heat.
• Clay and porcelain are poor conductors of heat — correct. Yes!
• Clay and porcelain make heat. Cups do not make heat. They only let it escape slowly.
• a metal. Metals are good conductors of heat.
• a flame. A flame is a source of heat, not a kind of material.
• an insulator — correct. Yes!