Simple Heat Conduction

Author: nitin.p070

Heat conduction or Thermal conduction is the transfer of energy between particles in a solid.Heat can also be transferred by Thermal radiation and/or convection and it is normal that more than one of these processes happen at the same time.

In the atomic theory solids, liquids and gases are made of tiny particles called atoms. The temperature of the material measures how fast the atoms are moving and the heat measures the total amount of energy due to the vibration of the atoms.

You might imagine conduction to take place when one part of a material is heated. The atoms in this part vibrate faster and are more likely to hit their neighbours.When collisions take place, the energy is passed on to the neighbouring atoms allowing the energy to travel through the solid. ( Rather like the way energy passes along a set of tumbling dominos.)

The atomic picture also helps explain why conduction is more important in solids: in solids the atoms are close together and unable to move around. In liquids and gases the particles can move past each other, so the collisions are less common
A thermos bottle is an excellent example demonstrating how all three methods are inhibited. A thermos bottle has a double wall that creates a vacuum, and a shiny surface inside of it. We've seen that the shiny part on the inside is an example of radiation, where heat is reflected back from the walls and back to the liquid. Heat conduction is inhibited by the use of insulators such as glass and plastic. Heat does escape, through the body and the lid, but very slowly. The vacuum inhibits convective currents and also conduction.

Grilling, broiling, and cooking over an open flame when you go camping are examples of cooking by radiation. However, when you grill and place your food on the grates, conduction also comes into play. When the air becomes hot, convection currents are created between the air and the food.

When you bake a cake or pot roast, all three methods are once again involved. There are convection currents as the air becomes hot from the oven. The pan the food is in becomes hot due to conduction. The walls of the oven become hot, and this is due to radiation.

We have previously seen that when you boil or steam food, the air and the water is heated by convection. Solid food, however, is heated by conduction, as the atoms inside of it begin colliding with each other.

Aside from cooking, there are simple heat transfer experiments you can do at home.

A Simple Heat Conduction Experiment

Obtain objects of different materials. Ideally, they would be of the same geometry, such as rods made from wood, glass, aluminum, and iron. However, materials such as plastic, wooden, and metal silverware will do. You will also need a heat source such as hot water, a stove burner, a hot plate, or a candle. To make the measurements, use a watch or some other time keeping device, and a simple thermometer. To record your results, use a spreadsheet or graph paper.

For a direct measurement, use masking or electrical tape to attach the thermometer to an object. Submerge it partially in hot water, and take time and temperature readings every few seconds. Graph the temperature versus time by placing the dependent variable, temperature, on the y axis and the independent variable, time, on the x axis. Do this for every object. Compare your results.

For indirect measurements, melt a substance such as candle wax or paraffin on the object. Slowly heat the object, and record the time it takes for the substance to melt. If you are careful, the substance can also be ice, butter, or something similar. In this case, the holder would have to be a spoon.

Remember to use caution whenever doing heat transfer experiments, as the objects and sources will be hot.

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