Categories
Physics

Heat energy – Transfer of Heat

Radiation, Emission and Radiation by Different Surfaces

Use this visual Slides to understand the concept of Heat Transfer before you proceed:

https://www.slideshare.net/slideshow/embed_code/key/NQAK0GFvGy9nUbCh22 heat transfer from Denisiu

Conduction of Heat

Meaning of Heat Conduction

Conduction of heat is the process by which heat is passed along a material from molecule to molecule while the heated particles remaining in mean position. Most metals are good conductors but their thermal conductivities differ from one metal to another. Experiment performed to compare the conductivity of solid showed that copper is a better conductor than brass, followed by iron, lead…

Using Kinetic Molecular Theory to Explain Conduction in Solids

conduction with Kinectic theory

When the end A is heated, molecule A vibrates about its mean position with a greater kinetic energy and pushes the molecule B to do the same. Molecule B’s increase in kinetic energy is transferred to C and so on until this effect reaches Z. Soon the kinetic energy of molecule at Z is also increased. As the kinetic energies of the molecules increase, temperature increases and heat is then transferred from the hot part to the cold part.

Conduction of Heat in Liquids

Liquids are poor conductors of heat except mercury and other molten metals. Experiment demonstrated below shows that water is a poor conductor of heat.

Experiment to Show that Water is a Poor Conductor of Heat

water poor conductor experiment

Aim: To show that water is a bad conductor of heat.

Apparatus: water, test tube, ice-block, Bunsen burner and wire guaze.

Method: i. Wrap the ice block with wire guaze to prevent the ice from floating in water, and drop in the water in the test tube.

  1. Heat the water near the top of the water with the Bunsen burner.

Observation: It is observed that while the water was boiling on top, the ice at the bottom did not melt

Conclusion: The ice did not melt because water is a poor conductor of heat and was not able to conduct the heat to the ice.

Applications of Conductors and Insulators

  1. Cooking utensils: Bad conductors of heat are used as handles while the cooking pots are made ofmetals such as aluminium which are good conductors of heat.
  2. Lagging: Insulators are often used as lagging materials in hot water pipes, stem boilers, hot water storage tanks and ovens to prevent them from getting colder.
  3. Warmth: Woollen sweaters keep us warm during winter or cold weather to prevent conduction of heat from the body.
  4. Double walls: Houses built with double walls with space in between them have air trapped in the spaces that act as insulators, thus, keeping the house warm.

EVALUATION

  1. What is conduction?
  2. Use the molecular theory to explain conduction.
  3. Explain three applications of conductors and insulators.

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