Conduction

Conduction is the process by which heat flows from the hot end to the cold end of a solid body without any net bodily movement of the particles of the body.

Solid substances that conduct heat easily are called good conductors of heat.

Substances that do not conduct heat easily are called bad conductors of heat.

Apparatus

• Bars of stainless steel (or iron), aluminium, and copper (each about 30 cm long, same shape)
• Candle, burner, pins

Procedure

1. Take stainless steel (or iron), copper, and aluminium bars, each about 30 cm long and having the same shape.
2. Apply wax spots using a candle at a distance of 2 cm from each other on all three bars.
3. Stick a pin in each wax spot so that it stands upright.
4. Insert the ends of all three bars into a flame at the same time.
5. Observe for a while — from which bar do the pins start falling first?

Experiment Diagram

Observation

• Pins fall starting from the end near the burner and progress toward the cold end.
• Pins on the copper bar start falling first.
• Pins on the steel bar fall comparatively late.

Conclusion

• Heat travels from the hot end to the cold end of the bar.
• Copper conducts heat quickly; steel conducts heat more slowly.
• The rate of heat conduction depends on the property (material) of the substance.
• Since heat travels through the solid bar, a medium is required for conduction.

When one end of a metal rod is placed in a flame while the other end is held in hand, the end held in hand slowly gets hotter — even though it is not in direct contact with the flame.

The process works as follows:

• When one end of the rod is heated, the molecules there vibrate faster.
• As they collide with their slow-moving neighbours, they transfer some of their energy to these molecules.
• Those molecules in turn transfer energy to their neighbouring molecules still further down the rod.
• In this way, the energy of thermal motion is transferred by molecular collisions down the rod.

When one end of a metal rod is placed in a flame and the other end is held in hand:

• The end held in hand slowly gets hotter, although it is not in direct contact with the flame.
• Heat has been conducted from the hot end to the cold end.

• The transfer of heat from the hot part to the cold part of an object is called conduction of heat.
• Conduction takes place through solid substances only — it requires a medium.
• Heat travels by molecular collisions: fast-vibrating molecules pass energy to slower neighbours.
• Copper conducts heat faster than aluminium, which conducts faster than steel.
• Conduction of heat through a substance depends on the property of that substance.
• Good conductors: silver, copper, aluminium, brass — all metals.
• Bad conductors: wood, cloth, air, paper — most non-metals.
• Good conductors of heat are also good conductors of electricity, and bad conductors of heat are also bad conductors of electricity.