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Heat & Temperature

Non - Invasive infrared thermometer A non–invasive infrared thermometer. It is a new thermometer that makes accurate measurements in just a single touch. The soft hollow site behind the ear is very close to the artery (that carries blood to the brain). This is used to make temperature measurement with the infrared thermometer. The image shows the temperature of a patient as recorded by it. What is the meaning of the value shown in the thermometer, and how is it related to heat? What are the different scales to measure the heat? What are the other sources of heat? Lets ponder as we discuss more of these in this topic.

Learning objectives

After completing the topic, the student will be able to:

  • Define, discuss and distinguish the terms heat and temperature.
  • Discuss, explore and examine different types of thermometers and temperature scales used to measure the temperature.
  • Illustrate Joule's experiment to prove that heat is a form of energy.
  • Define and explore the concept of specific heat and its relevance to everyday science.
  • Calculate the amount of heat absorbed by a body and illustrate the significance of molar specific heat to the real world applications.
  • Analyze and illustrate the experiment of calorimeter and its types, to measure the amount of heat exchange.
  • Discuss and investigate different types of sources of heat and explore the changes that take place in an object due to heat produced.
  • Discuss and investigate the working of thermostat used in refrigerators.
  • Explore the concept of combustion and investigate its requirements.
  • Analyze the criteria for the combustion of a fuel.
  • Explore the process behind the survival of the humans by the Intake of food.

Atoms movement Atoms movement due to thermal energy. Vigorously rubbing the desktop with an eraser generates heat by transferring mechanical energy to thermal energy. You feel this as warmth. Molecules vibrate when heated. As the temperature rises, the particles have more kinetic energy and vibrates vigorously.

Energy comes in various forms. Light, sound, mechanical energy, electrical energy, etc, are all different forms of energy. As we know, energy (and mass) can never be created or destroyed but it can be converted from one form into another.

Matter is composed of atoms and molecules. Atoms inside the molecules are never stationary. By virtue of their motion matter possesses kinetic energy. The average kinetic energy of the individual particles is directly related to a property you can sense: How hot something is. Whenever kinetic energy of its particles increases the substance becomes warmer.

Strike a coin with a hammer and it becomes warm because the hammer's blow causes the atoms in the metal to jostle faster. Rapidly compress air in a tyre pump and the air becomes warmer.

Stretch a rubber band and hold it on your lip; you will feel that it has become warmer. Heat and temperature are different quantities, although they are related to one another. Heat is the cause; temperature change is its effect.

Energy Transfer Energy transfer creates steam Energy (heat) is transferred from the iron to the water causing water molecules near the surface to boil off and condense into steam. The energy transfer continues until the iron and the water are in a state of equilibrium (have the same temperature).
Heat and internal energy

If you take a can of cola from the refrigerator, energy passes out of your hand and into the colder cola can. In the same way if you touch a cup of hot coffee, energy enters your hand because the coffee is warmer than your hand. The direction of spontaneous energy transfer is always from a warmer object to a neighbouring cooler object. The energy transferred from one object to another because of a temperature difference between them is called heat.

Matter contains molecular kinetic energy and potential energy. Heat is energy in transit from a body of higher temperature to another body of lower temperature. Once transferred, the heat energy ceases to be known as heat!

Let us now see why should a body transfer heat energy to another body.

In a substance there is potential energy due to the forces between molecules. There is rotational kinetic energy of molecules and kinetic energy due to internal movements of atoms within molecules. In addition there is translational kinetic energy due to jostling of molecules in a substance. All these energies inside a substance are collectively known as internal energy. In short, a substance does not contain just heat – it contains internal energy.

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