Conduction of Heat

• Conduction — heat transfer through solids by direct contact without bulk movement of the material.
• Good conductors (metals) vs insulators (wood, plastic, wool, air) — why handles are plastic and pans are metal.
• Heat flows from the hotter end to the colder end of a solid until temperatures equalise.
• NCERT wax-on-metal-rod activity showing heat travelling along a strip.
• Everyday Indian examples: iron tawa, stainless steel pressure cooker, woollen shawl in Shimla.
• How trapped air gaps in wool, thermos flasks, and hollow bricks reduce heat loss.

Level 1 — Core idea

1. Conduction — particles at hot end vibrate faster and pass energy to neighbours.

2. Metals — free electrons carry heat quickly; best conductors: silver, copper, aluminium, iron.

3. Insulators — wood, rubber, plastic, glass wool, wool, styrofoam, trapped air.

Level 2 — Process and representation

1. Diagram (text) — metal rod heated at left end; wax pins fall one by one from hot end toward cold end.

2. Cooking pan — metal base conducts heat from flame to food; plastic/wooden handle insulates.

3. Woollen clothes — trap air; air is poor conductor → less heat loss from body in winter.

Level 3 — Applications and NCERT links

1. Double-walled thermos — vacuum between walls stops conduction (and convection).

2. Same temperature, different feel — metal feels colder than wood at 25 °C because metal conducts heat away from skin faster.

3. NCERT Activity — wax pieces on metal strip over flame; order of falling shows conduction path.

NCERT Activity: Wax pieces on a metal strip (Activity 4.2)

Materials: metal strip, wax, pins, candle/flame, stand.
Step 1 — Fix wax-coated pins at equal intervals along a horizontal metal strip.
Step 2 — Heat one end of strip over flame gently.
Step 3 — Pin nearest flame falls first (wax melts), then next, then next — sequential order.
Step 4 — Pin farthest from flame falls last — heat travelled along strip by conduction.
Step 5 — Repeat with a wooden strip: pins do not fall quickly — wood is insulator.
Step 6 — Compare: heat reaches distant points slower in poor conductors.
Step 7 — Safety: do not touch heated metal; use test-tube holder.
Conclusion: metals conduct heat; heat flows from hot end to cold end through solids.

• Define conduction in one sentence.
• Name one good conductor and one insulator.
• Why are cooking pans made of metal but handles of plastic/wood?
• Why does wool keep us warm?
• In the wax activity, which pin falls first and why?
• Why do we wear woollen clothes in Shimla winters?

Open the Practice tab for graded questions on Conduction of Heat.