# 1st Year Physics Notes Chapter 4 - 11th Class Notes pdf

Looking for the notes of Physics class 11 chapter 4 Work and Energy. Here we have uploaded the 1st Year Physics Notes Chapter 4 - 11th Class Notes pdf download or read online Topics notes, Short and long questions and exercise questions.

Unit of Power
Power is a scalar quantity
Si unit of power is joule/second called watt.
Dimension of power is [MLT'
Definition of Watt
The power is said to be one watt if one joule of work is done in one second
Q. How absolute potential energy changes with distance r from the centre of earth increases?
. When body moves away from earth increases, the gravitational force does negative work and U increases (i e it becomes less negative
When the body moves falls toward the earth, r decreases, the gravitational force does positive work and U decreases (ie it becomes more negative)
Note: (Zero reference point)
The choice of zero point is arbitrary
We can take the surface of the earth or the point at infinity is zero P E reference The difference of P E from one point to another is significant The change in P E as we move a body above the earth's surface will always positive
Q. State law of conservation of energy. Why new sources of energy has to be developed if energy is conserved?
Conservation of energy
Statement
Energy cannot be destroyed it can be transformed from one form into another, but the the total amount of energy remains constant.
Conservation of mechanical energy
The KE and PE are the different forms of mechanical energy The total mechanical energy of the body is equal to the sum of KE and PE
PE may change into K E Similarly, the K E may also be change into PE, but total energy remains constant
Mathematically total energy PE KE = constant
This is the special case of conservation of energy
Need for new sources In daily life we observe many energy changes from one form to another At last all energy transfers the heat to the environment and energy is lost in the form of heat which is useless So, useful energy is decreasing through total energy is conserved That's why we need to develop new sources of energies
Q. Discuss the different non-renewable energy sources.
Non-renewable Energy Sources
These sources are not very common these days Some of them are given below Coal
Coal is a solid form fossil fuel that can be classed into three types lignite bituminous and anthracite Lignite coal is found close to the Earth surface, making it easy to mine but it has high Sulphur content Bituminous coal is the most common coal we burn, and it is less polluting than lignite Anthracite
the Earth the highest quality of coal-it is dark and shiny and found deeper
Oil
Oil is a liquid fossil fuel that can be dark brown, yellow or even green It is easier to mine once it is found because, being a liquid it will flow through pipes, which makes it easier for transport However it can be difficult to locate oil forms in reservoirs and to find these reservoirs scientists must study rocks and landforms to find potential drilling sites
Once a hole is called and oil is found, it s then piped to the surface In this form, it is called crude OH Crude oil is transported to a refinery that heats up the oil to different temperatures and sorts out the different types of fuel (such as petrol jet-fuel and diesel) through a process called fractional distillation Oil is used not just for transport but also in many different products such as plastics, tyres and synthetic material such as polyester.
Natural gas
As the name suggests this is a fossil fuel in the form of a gas (for example, methane and LPG). It is often found under the oceans and near oil deposits Surveying for natural gas reservoirs is similar to oil exploration Once a natural gas field is found the drilling process is similar to oil Gas can be piped from the source and stored for later use Natural gas is used for cooking and heating as well as making a number of products such as plastics fertilisers and medicines
Q. Discuss the different Renewable energy sources.
Renewable energy sources
Energy from tides
Gravitational force of moon produces tides in the sea The tide raise the water n the sea rough two times a day
Explanation
Water at high tide can trapped in a basin by constructing a dam.
Dam is filed at high tide
Then water is released in a controlled wayat low tide to derive the turbines The dam is filled again for next high tide and the fall of water also derive the turbines . This process is used to generate the current
Energy from waves
The tides and waves blow across the surface of ocean
These waves produce strong water waves
The energy of these waves can generate electricity
Salter's duck The device which is used for this purpose was invented by Professor Saiter called Salter s duck It has two parts (i) Duck float (ii)Balance float
The wave energy produces the movement in duck float relative to balance float The relative motion of duck float is used to run electricity generators
Solar energy
Sun is the major source of energy on earth Solar energy at normal incidence outside the earth's atmosphere is about 1 4KW/m Which is called solar constant While passing through atmosphere the total energy is reduced due to reflection. scattering and absorption by dust particles water vapors and other gases
On a clear day at noon, the solar energy at the surface of the earth is 1KW/m Solar energy is used to heat the water by solar reflection and thermal absorbers It can also used to generate electrical energy
For this purpose, the surface of the collector is blackened to absorb the heat energy it can heat up the water up to 70°C1o ge higher temperature, we use the reflectors or lens of larger size Sunlight can be converted into electrical energy by photovoltaic cells. They are made up of silicon Electrons in the silicon gains energy from sunlight to create voltage Solar panel are expensive but of long life time and have low running cost
Electric energy
Energy from water power is very cheap Dams are being constructed at suitable locations in different parts of the world Dams serve many purposes They help to control floods by storing water The water stored in dams is used for irrigation and also to generate electrical energy without creating much environmental problems
Wind energy:
Wind has been used as a source of energy for centuries It has powered sailing ships across the oceans It has been used by windmills to grind grain and pump water More recently, wind power is used to tum wind turbines. When many wind machines are grouped together on wind farms, they can generale enough power to operate a power plant.
In the United States some wind farms generate more than 1300 MW of electricity a day in Europe many wind farms routinely generate hundred megawatts or more electricity a day
Energy from Biomass:
it includes the organic materials such as crop residue, natural vegetation, trees, animal dung and sewage. Biomass energy refers to the use of materials as fuel Two common methods of conversion of biomass into fuels are direct combustion and fermentation
Direct combustion method
Direct combustion method is applied to get energy from waste product commonly known as solid waste and confined it into chamber and ignite it The heat product is then use in a boiler to run the turbine of generator
Fermentation Method:
Bio fuel such as ethanol is a replacement of gasoline, which is obtained by fermentation of biomass using enzymes and by decomposition through bacterial action in the absence of air The rotting of biomass in a closed tank called a digester produces Biogas which can be piped out to use of cooking and heating
Geothermal Energy:
The heat extracted from inside the earth is in the form of hot water or steam, It can be generated by following methods
Due to decay or radioactive elements, the energy heating the rocks is constantly being released Residual Heat of the Earth
Hot igneous rocks within 10 km of the earth are present in molten form They conduct heat energy from interior part of the earth. The temperature of these rocks is 200°C or more
Compression of Material:
in deep inside the earth, the compressed materials cause for the generation of heat energy In some places water beneath the ground is in contact with hot rocks and is raised to high temperature and pressure in form of hot springs, geysers or steam vents The steam produced in this way can run the turbines or for heating purpose
Geo thermal energy may cause to produce hot geyser releasing with an explosive column into the air The usually occur in volcanic region and erupt with irregular intervals This extraction of geo thermal seriously disturbs geyser system by reducing heat flow and aquifer pressure Aquifer is a layer o rock holding water that allows water to percolate through it with pressure Nuclear Fuels:
In nuclear power plants, we get energy as a result of fission reaction During fission reaction heavy atoms, such as Uranium atoms split up into smaller parts releasing a large amount of energy Nuclear power plants give out a lot of nuclear radiations and vast amount of heat A part of this heat is used to run power plants while lot of heat goes waste into the environment

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