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Topic Content:

  • Meaning of Conduction
  • Experiment to show that Water is a Poor Conductor of Heat
  • Experiment to Compare Thermal Conductivity of Different Materials (Ingen Hauz’s Experiment)
  • Using Kinetic Molecular Theory to Explain Conduction in Solids
  • Application of Conductors & Insulators

It is a common experience that when hot water is poured into a stainless cup, the cup becomes hot after a few minutes as a result of heat transfer from the hot water to the stainless cup; this process of heat transfer is called conduction.

Conduction is a process of heat transfer through a material, with the average position of the particle material remaining the same.

It depends on the difference in temperature of the hot and cold body for conduction to take place. The materials involved must allow heat energy to pass through them and such materials are called conductors.

A conductor is a substance that allows heat energy to flow through it e.g. most metals are good conductors of heat.

An insulator is a substance that does not allow heat energy to flow through it e.g. wood, plastic, rubber, and wool.

Experiment to show that Water is a Poor Conductor of Heat:

Set up:

Experiment to show that Water is a Poor Conductor of Heat

Aim:

To demonstrate that water is a poor conductor

Apparatus:

Big test tube, metal gauge, water, heat source, metal wire.

Procedure:

  • This is achieved by wrapping an ice block in a metal gauze and placing it in a test tube full of water.
  • The tube is placed in a slant position or tilted and the water on the top of the test tube is heated until the water starts boiling.

Observation:

It will be observed that as the water on the top part of the test tube is boiling, the ice block at the bottom of the tube remains unaffected which shows that water is a poor conductor of heat.

Conclusion:

Water is a poor conductor which was the reason that the ice block at the bottom of the tube was unaffected.

Experiment to Compare Thermal Conductivity of Different Materials:

Ingen Hauz Experiment conductivity

Aim:

Ingen Hauz’s Experiment – To compare the thermal conductivities of different materials.

Apparatus:

Gold, lead, aluminium, iron, copper and silver rods, rectangular box or trough and hot water. 

Procedure:

  • Coat rods of equal length of gold, lead, aluminium, iron, copper and silver coated with a thin layer of wax of uniform thickness.
  • Insert the rods in a rectangular box or trough as shown in the diagram above.
  • Pour boiling water into the trough.

Observation:

After some time the rods absorb heat and the wax on them starts melting. It is observed that the length of the melted wax differs for all the rods. The wax left on silver is the smallest which means that the silver melted the most, followed by copper and gold. Lead is the least conductive because only a small amount of the wax melted.

Conclusion:

Thus, one can conclude that the rate of conduction is different for different metals. Silver has the highest thermal conductivity, followed by silver, gold, aluminium and lead.

Using Kinetic Molecular Theory to Explain Conduction in Solids:

conduction

When one end of a solid is heated, the molecule at the particular end gains kinetic energy and vibrates strongly about its mean position. As it vibrates faster and faster about its mean position, it collides with neighbouring particles and causes those molecules to vibrate about their mean position too.

As the kinetic energies of the molecules increase, temperature increases and heat energy is transferred to the molecules one after the other, from one end of the solid to the other end.

Application of Conductors & Insulators:

  • Cooking pots are made of a material that can conduct heat quickly (aluminium) while their handles are made up of insulators (wood and porcelain).
pot
Cooking pots conduct heat while their handles are insulators e.g. plastic.

  • Carpets and rugs are used at home and offices to keep the feet warm being insulators. While tiles and marbles conduct heat away from our feet, hence, our feet feel cold when we walk barefooted.
  • During hot periods, houses with thatched roofs keep warm as compared to houses with concrete roofs. It is because thatched roof contains a large amount of trapped air which is a bad conductor of heat. As a result, heat from outside does not flow into the thatched roof house.
  • Woollen clothes keep us warm during winter or cold weather. They prevent the conduction of heat from the body.