Section 4: Energy resources and energy transfer ​

(a) Units ​

4.1 use the following units: kilogram (kg), joule (J), metre (m), metre/second (m/s), metre/second2 (m/s2), newton (N), second (s), watt (W).

Unit of mass: kilogram(kg) Unit of energy: joule(J) Unit of distance: metre(m) Unit of speed or velocity: metre/second (m/s) Unit of acceleration: metre/second²(m/s) Unit of force: newton (N) Unit of time: second (S) Unit of power: watt(W)

(b) Energy transfer ​

4.2 describe energy transfers involving the following forms of energy: thermal (heat), light, electrical, sound, kinetic, chemical, nuclear and potential (elastic and gravitational)

Thermal energy: The energy which is released by a hot object when it cools down is called thermal energy. E.g: If we rub our hands together, kinetic energy will transform into thermal energy.

Light energy: The energy which is released from luminous object is called light energy. E.g.: In a filament lamp, electrical energy is converted to heat energy and light energy.

Electrical energy: The energy of charged object is called electrical energy. E.g.: In an electric generator, kinetic energy is converted to heat and electrical energy.

Sound energy: The energy by which we can hear is called sound energy. E.g.: Clapping our hands will convert kinetic energy to sound and little amount of heat energy.

Kinetic energy: The energy of a moving object is called kinetic energy. E.g.: In a ceiling fan, electrical energy is converted to kinetic energy.

Chemical energy: The energy which is released by chemical reaction is called chemical energy. E.g: In a motor car, chemical energy is converted to heat, electrical and kinetic energy.

Nuclear energy: The energy which is released by nuclear reaction is called nuclear energy. E.g.: Energy is nuclear power stations.

Potential energy: The energy which is gained by changing size, shape and position of an object is called potential energy. E.g: Raise a ball 10m above ground, it will gain gravitational potential energy.

4.3 understand that energy is conserved

Energy is not created or destroyed in any process. It is just converted from one from type to another.

Wasted energy: When we try to do things, there is some energy converted to unwanted forms. This form of energy is known as wasted energy.

4.4 know and use the relationship:

Effeciency is the ratio of useful energy output and the total energy input.

effeciency=useful energy outputtotal energy input x 100%

4.5 describe a variety of everyday and scientific devices and situations, explaining the fate of the input energy in terms of the above relationship, including their representation by Sankey diagrams

Whenever we are transferring energy, proportion of input energy is wasted. Like a lamp has input energy of 100J. It uses 10J to give light and the other 90J is wasted as heat.

effeciency=useful energy outputtotal energy input x 100%

effeciency=10J100J x 100%

effeciency=0.1%

In a Sankey diagram it is presented like this:

4.6 describe how energy transfer may take place by conduction, convection and radiation

There are three basic ways energy can transfer from place to place: conduction, convection and radiation.

Conduction: Thermal conduction is the transfer of heat energy through substance mainly metals, without the substance itself moving. They transfer energy through molecular vibration or free electron diffusion.

Metals are good conductors of heat but non-metals and gases are usually poor conductors of heat. Poor conductors are called insulators. Heat energy is conducted from the hot end of an object to the cold end.

Heat conduction in metals The electrons in piece of metal can leave their atoms and move about in the metal as free electrons. The parts of the metal atoms left behind are now charged metal ions. The ions are packed closely together and they vibrate normally continually. The hotter the metal, the more kinetic energy these vibration have. The kinetic energy is transferred from hot parts of the metal to cooler parts by the free electrons. These move through the structure of the metal, colliding with ions as they go.

Convection: Convection is the transfer of energy by means of fluids (liquids or gases) by the upward movement of warmer, less dense region of fluid.

The particles in fluids can move from place to place. Convection occurs when particles with a lot of heat energy in a liquid or gas move and take the place of particles with less heat energy in a liquid or gas move and take the place of particles with less heat energy. Heat energy is transferred from hot places to cooler places by convection.

Liquids and gases expand when they are heated. This is because the particles in liquids and gases move faster when they are heated than they do when they are cold. As a result, the particles take up more volume. This is because the gap between particles widens, while the particles themselves stay the same size.

The liquid or gas in hot areas is less dense than the liquid or gas in cold areas, so it rises into the cold areas. The denser cold liquid or gas falls into the warm areas. In this way, convection currents that transfer heat from place to place are set up.

Radiation: Radiation is the transfer of energy by means of wave (Infra-red). It doesn’t need any medium to flow through. It travels at the speed of light and is actually a specific part of this family of electromagnetic waves. So radiation is the continual emission of infrared waves from the surface of all bodies transmitted without the aid of medium.

4.7 explain the role of convection in everyday phenomena

1. Household hot-water systems

The working principle of the household hot-water system which is based on the convection in liquids is as follows:

Water is heated in the boiler by gas burners. The hot water expands and becomes less dense. Hence, it rises and flows into the upper half of the cylinder.

To replace the hot water, cold water from the cistern falls into the lower half of the cylinder and then into the boiler due to the pressure difference.

The overflow pipe is attached to the cylinder just in case the temperature of the water becomes too high and causes a large expansion of the hot water.

The hot-water tap which is led from the overflow pipe must be lower than the cistern so that the pressure difference between the cistern and the tap causes the water to flow out of the tap.

2. Electric kettles.

The heating coil of an electric kettle is always placed at the bottom of the kettle.

When the power is switched on, the water near the heating coil gets heated up, expands and becomes less dense. The heated water therefore rises while the cooler regions in the upper part of the body of water descend to replace the heated water.

3. Air-conditioners

The rotary fan inside an air-conditioner forces cool dry air out into the room. The cool air, being denser, sinks while the warm air below, being less dense, rises and is drawn into the air-conditioner where it is cooled. In this way, the air is recirculated and the temperature of the air falls to the value preset on the thermostat.

4. Refrigerators

Refrigerators work in very much the same way as air-conditioners. The freezing unit is placed at the otp to cool the air so that the cold air, being denser, sinks while the warm air at the bottom rises. This sets up convection currents inside the cabinet which help to cool the contents inside.

4.8 explain how insulation is used to reduce energy transfers from buildings and the human body.

The bigger the difference in temperature between an object and its surroundings, the greater the rate at which heat energy is transferred. Other factors also effect the rate at which an object transfers energy by heating. These include the:

• Surface area and volume of the object. If we compare two objects of the same mass and made of same material, but having different surface areas, the object with the larger surface area will emit infra-red radiation at a higher rate.
• Material used to make the object. A conductor conducts heat away more quickly than a insulator. The better its conductivity, the faster it will release heat.
• Colour and texture of the surface Dull, black surfaces are better emitter of infrared radiation than shiny, white surfaces.
• Surface temperature The rate of transfer of energy by radiation also depends on the surface temperature. The higher the temperature of the surface of the object relative to room temperature, the higher the rate of energy transfer.

Energy efficient houses and insulation Reduce heat transfer by conduction:

• Use a vacuum: Conduction needs matter; used in vacuum flasks, some types of double glazing etc.
• Use air: Air is a good insulating material. Many materials like wool, feathers, furs etc. trap air so it cannot circulate. This works because air is a very poor conductor of heat. Houses use fibre glass insulation and cavity walls are sometimes filled with a foam (again, to stop circulation by convection).
• Use water: Wetsuits trap a layer of water around the body because water is a poor conductor.

Reduce heat transfer by convection:

• Use a vacuum: Convection needs gases or liquids, used in vacuum flasks, some types of double glazing, etc.
• Use trapped gas or liquid. This restricts circulation, which is necessary for convection to occur. The size of gap between the sheets of glass is a compromise. A narrow gap makes the effect of convection smaller, but it allows a greater amount of heat transfer by conduction.

Reduce heat transfer by radiation:

• Use shiny surfaces: Very shiny surfaces reflect (heat) radiation well. Fire fighters wear shiny suits to stop heat radiation getting to their bodies. Shiny surfaces are also poor radiators of heat. Space blankets, for example, retain the body heat of athletes or hill-walkers suffering from exposure. This is because they have a shiny inner surface which reflects heat back to the person and also a shin outer surface which is a poor radiator of infrared.

Other measures:

• Thermostats and computer control systems for central heating can further reduce the heating needs of a house. They stop rooms being heated too much by switching off the heat when a certain temperature is reached.
• Reduction or elimination of draughts from poorly fitting doors and windows.

(c) Work and power ​

4.9 know and use the relationship between work, force and distance moved in the direction of the force:

Energy is the ability to do work.

work=force x distance

W=F x d

1J of work is done when a force of 1N is applied through a distance of 1m in the direction of the force.

4.10 understand that work done is equal to energy transferred

Doing work means the energy is either decreased or increased. If a weight of 500N is raised 2m, 1000J of work is done. That means energy is increased by 1000J. Therefore work done is equal to energy transferred.

4.11 know and use the relationship:

The energy that the weight has gained is called gravitational potential energy.

gravitional potential energy=mass × gravitional acceleration × height

G.P.E=mgh

4.12 know and use the relationship:

Kinetic energy = ½ x mass x velocity²

K.E = ½ x m x v²

4.13 understand how conservation of energy produces a link between gravitational potential energy, kinetic energy and work

An object of mass,m weights mxg newtons. So the force,F, needed to lift is mg. If we raise the object through a distance h, the work done on the object is mgh. This is also the gain of GPE.

When the object is raised, it falls-it loses GPE but gains KE. At the end of the fall, all the initial GPE is converted into KE. And that’s how energy is conserved.

work done lifting object=gain in GPE=gain in KE of the object just before hitting the ground

4.14 describe power as the rate of transfer of energy or the rate of doing work

Power is the rate of transferring energy or doing work. Its measures how fast energy is transferred. The Watt is the rate of transfer of energy of one joule per second.

4.15 use the relationship between power, work done (energy transferred) and time taken:

power=work donetime

P=Wt

(d) Energy resources and electricity generation ​

4.16 describe the energy transfers involved in generating electricity using:

• Wind: Winds are powered by the Sun's heat energy. Wind is a renewable source of energy. Wind mills have been used to grind corn and power machinery like pumps drain lowland areas. Today, wind turbines drive generators to provide electrical energy. Here, kinetic energy is transformed to electrical energy.
• **Water:**Water is used to generate energy in three ways: Hydroelectric power, Tidal power & Wave energy. All the ways uses the same role using the movement of water(K.E.) to rotate that generator and produce electricity. In this casekinetic energy is also transformed to electrical energy.
• Geothermal resources: Geothermal energy is heat energy stored deep inside the Earth. The heat in regions of volcanic activity was produced by the decay of radioactive elements. The heated water from the earth’s crust is used to rotate turbines in generator. Here, heat energy is converted to kinetic energy which is converted to electrical energy.
• Solar heating systems: Solar heating panels absorb thermal radiation and use it to heat water. The panels are placed to receive the maximum amount of the Sun’s energy.This produce steam which can be used to drive electricity generators.
• Solar cells: Solar energy directly converts light energy into electrical energy.
• Fossil fuels: Fossil fuels are natural gas, oil and coal. Those are burned which rotates the turbine in the generator to produce electricity.
• Nuclear power: Nuclear fuels like uranium are used in nuclear generator. The heat produced in nuclear reaction is used to produce steam from water which rotates the turbine and produce electricity.

4.17 describe the advantages and disadvantages of methods of large- scale electricity production from various renewable and non- renewable resources.

Renewable Resources:

Non-Renewable Resources: