Heat – Transfer of Heat
* Heat flows from a hotter object to a colder object.
* He heat flows a hot body is gradually transferred the particles of the surrounding air that are comparatively cooler.
* The process by which heat is transferred from the hotter part to the colder part of an object, without the movement of the particles of that object, is known as conduction. Conduction occurs only in solids.
* Materials that do not allow heat to pass through them are called conductors.
* Convection is the transfer of heat by the movement of particles of the medium from one place to another. Convection takes place only in liquids and gases.
* The weather in coastal areas is generally temperate because of land and sea breezes.
* Land heats up and cools faster than air and water. Land sea breezes are a result of convection of heat in the air.
* Radiation is a process in which heat is transferred from one object to another either through a medium or vacuum.
* Heat absorbed by object from their surroundings increases their temperature.
Sources of Energy
* A non – renewable source of energy is one that cannot be replenished in a short period of time.
Non – renewable fuels are classified as:
* Fossil fuels like coal, oil and natural gas.
* Nuclear fuels like uranium, tritium and thorium.
* A renewable source of energy is one that can be replenished within a short period of time.
Renewable source of energy can be classified as:
* Solar energy
* Wing energy
* Hydro energy
* Biomass energy
* Geothermal energy
* Tidal energy
* Ocean thermal energy
* A good source is one that enables us to do a large amount of work per unit volume or mass, is accessible, economical and easy to store and transport.
Temperature and Heat
* Heat is defined as a form of energy that flows from a hotter body colder body when they are in thermal contact.
* When two bodies are in thermal contact and there is no net exchange of heat, then they are said to be in thermal equilibrium.
* The physical quantity that is same for the systems in the thermal equilibrium is temperature.
* The SI unit is “joule” and temperature is “Kelvin”.
Conduction
* Transfer of heat takes place through conduction, convection and radiation.
* Thermal conduction is a mechanism of heat transfer between two bodies in thermal contact.
* Thermal conductivity depends on the state and nature of the substance.
* Change in temperature per unit length is defined as the temperature gradient.
* The SI of the thermal conductivity Js-1 m -1 k-1 or Wm-1 k-1.
Nuclear Energy
* When tightly bound nuclei transform into relatively less tightly bound nuclei, nuclear energy is released.
* The nuclear energy obtained for the same mass is enormous compared to that of the conventional sources of energy.
* When neutrons are bombarded into various elements, new radioactive elements can be produced.
* A nuclear fission process generates an enormous amount of heat energy.
* Nuclear fission products are highly rich in neutrons, and are unstable and radioactive. They emit beta particles in succession until they reach a stable end – product.
Energy Flow In Ecosystem
* Photo synthetically Active radiation or PAR is the spectral range of solar radiation that can be used by green plants for photosynthesis.
* In nature, there are two types of food chains – Grazing Food Chain and Detritus
Food Chain.
* All organisms in a food chain occupy a specific place depending their source of food and nutrition, which is known as their trophic level.
* Standing crop is the mass of living material at a particular time at each tophic level.
* The transfer of energy follows a ten – per cent law, that is , an average only tenpercent of energy is transferred from one trophic level to another.
Greenhouse Effect and Global Warming
* The greenhouse effect is the heating of the earth’s surface due to greenhouse gases such as carbon dioxide, methane, nitrous oxide and ozone.
* Continuous heating of the earth due to the greenhouse effect has resulted in global warming.
* The rise in the earth’s temperature is resulting in odd climatic changes such as the El Nino effect and melting of polar and mountain ice caps.
* The melting of glaciers and snow caps will result in a rise in sea level, which could submerge many coastal areas.
* A reduction in the use of fossil fuels and deforestation can help reduce global warming.
* Optimal utilisation of energy and planting trees can reduce greenhouse gases.