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1. In physics and chemistry, heat is energy transferred from one body to another by thermal interactions. The transfer of energy can occur in a variety of ways, among them conduction,radiation, and convection. The SI unit of heat is the joule. Heat can be measured by calorimeter, or determined indirectly by calculations based on other quantities, relying for instance on the first law of thermodynamics. In calorimeter, the concepts of latent heat and of sensible heat are used. Latent heat produces changes of state without temperature change, while sensible heat produces temperature change heat, energy that is transferred from one body to another as the result of a difference in temperature. If two bodies at different temperatures are brought together, energy is transferred—i.e., heat flows—from the hotter body to the colder. The effect of this transfer of energy usually, but not always, is an increase in the temperature of the colder body and a decrease in the temperature of the hotter body. Units of Heat Energy

Heat being a form of energy can be measured. What is the unit of heat energy? In CGS system, heat is measured in calories. Calorie is defined as 'the heat energy required to increase the temperature of 1gm of water through one degree Celsius'. In SI system, heat energy is measured in joules (J). Infact, in SI system all forms of energy is measured in joules. One calorie = 4.185 joules.

A larger unit called Kilocalorie is also in use. 1 kilocalorie = 1000 calories. Energy contents of food is usually measured in kilocalories. The calories counted in food are actually kilocalories. For example, the energy value of 100 g of baked potato is equal to 100 calories or 100 kilocalories. 2. Sources of heat

* The Sun
The sun is a part of our solar system. Thus, it is a natural source of heat energy. Sunlight is important for the existence of all living organisms on the planet. This form of heat energy is also called solar energy. Sun is a natural source of energy. Solar heat energy is essential for the survival of all forms of life on earth. Solar energy is considered as an alternate source of energy. * The Earth

The heat energy that is found from the Earth is called geothermal energy. Sustainable and clean geothermal energy can be found in the hot water and rocks present in the shallow ground. It is also found in the molten rocks available in the extreme depth of the Earth. * Air

The air around us is a very common source of heat energy for heat pumps. Exhaust air is also a good heat source for heat pumps in buildings, both commercial and residential. * Burning Fuels
Heat energy can be generated by the burning of fuels. Fuel can be defined as any combustible substance that can burn and provide energy. A few examples of fuels are wood, kerosene, coal, charcoal, gasoline/petrol and oil.

* Electricity
Electricity is a form of energy that can be converted into heat energy, thus, it's considered a source. For example, the clothes iron that is used in our domestic household uses electrical energy to generate heat.

* Waste Heat Recovery
Waste heat recovery is a process in which heat energy that is excess for certain industrial processes is diverted to use in other work applications. There are many industrial applications that generate large amount of excess heat. Waste heat recovery boilers are used to channel this excess heat into other useful work applications.

* Waste Water
Waste or effluent water is a possible source of heat energy as it has a constant high temperature throughout the year. For example, untreated and treated water from sewers and industrial waste water and condenser heat that is generated from refrigeration plants are used in making of electricity and other industrial processes.

3. Effect of heat-expansion.
4. Disease encounter during summer.
Sunburn refers to the burn caused to a living tissue such as the skin due to overexposure to ultraviolet...
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