4. Types of current.

Some electrical devices use batteries and some must be connected to the electric mains. Both provide electricity, but in different ways.

4.1. Direct current.
Between the terminals of battery, there is a continuous, stable flow of energy, if we use a voltemeter to measure the current in a car battery, the result will always be 12 volts. This is called direct current. In the same way, if we connect a light bulb to a battery, the electrons always flow in the same direction with the same current.

3. Types of circuits.

3.1. Series circuit.
Two or more elemts form a series circuit when the output of one element provides the input for the next element.
In the following diagram, the same current flows through all the elements, and the total voltage is the sum of the tensions at the end of each element.

3.2. Parallel circuit.
In a parallel circuit, the various components share the same input and output. In other words, the wires from both sides are joined together. In this case, the potential difference is the same for each element, but the current that flows through each brach is different.

3.3. Combination circuit.
A combination circuit has some elements connected in series and other elements connected in parallel.
In this tuype of circuit, the current remains constant between elements that are connected in series.

2. Elecrical quantities.

2.1. Voltage or potential difference.
The amount of energy that a generator can transfer to electrons depends on its voltage (V) or electric tension. This is measured in Volts (V).

If we want to measure voltage, we can use a voltemeter. This device has two wires that must be connected in parallel to the element that we are checking.


2.2. Measuring electrical current.
Electric current (I) is the charge or number of electrons that flow through the cross-section of a connductor every second.
                                    I = Q/t

Electric current is measured in amperes or amps  (A) in the international System or SI.

2.3. Electrical resistance: Ohm's Law.

CIRCUIT          VOLTAGE             ELECTRIC CURRENT             V/I  
      A                     3V                              30 mA                                 100
      B                     6V                              60 mA                                 100
      C                     9V                              90 mA                                 100

The resistance (R) of a material is equal to the volatge divided by the intensity of the electric current which travels through the material. The ratio, which is called Ohm's Law can be expressed as follows:
          R= V/I

2.4. Electrical energy and power.

• Electrical energy: if an electric current flows at a particular tension for a certain amount of time, we can calculate the energy that is consumed E = V x I x t
• Electric power: P = VxI

1. An electric circuit.

An electric circuit is a parthway for the flow of electrons, it consists of the following parts, which are connected by wires: a generator that provides energy, elements that provide conrol and protection; loads that receive and use energy.
Electric current is a continuous flow of electrons through a circuit.

1.1. Parts of an electric circuit.
Electric circuit consists of varoious parts:

• Generators.

-Cells and batteries.

• Loads. 

-Light bulbs: they produce light.
-Motors: they produce movement.
-Resistors: They produce heat.
-Bells: they produce sound.

• Switching devices.

-Switches.
-Push buttons.
-3-way switches.

1.2. Diagrams and symbols.

Unit 7: Electric circuits and electronics.

1. An electric circuit.
2. Electrical quantities.
3. Types of circuits.
4. Types of current
5. Effects of electric current.
6. Electromagnetic mechanisms.
7. Electromagnetic control systems.
8. Electronics.

8. How can we save energy?

There are two important ways we can save energy: by increasing the energy efficiency of devicees that we use and by recycling as much as possible.

8.1 Energy efficiency.
One of the best ways to save energy is to use devices that are more energy-efficient.
An energy-efficient device require less enrgy to perform the same work.
We can apply strategies of energy efficiency in many areas of daily life. In this way, we can significantly reduce the amount of energy that we consume.

• Lighting
• Domestic appliance.
• Air conditioning and heating.
• Transport.

8.2. Recycling.

Our consumption of manufactured products generates waste and uses energy. We can reduce these negative effects by recycling as much as possible.

When we recycle products, we avoid the extraction and processing of more natural resources. In this way, we can save enormous amounts of energy. 

Recycling old batteries saves energy, but it is also important because batteries contain toxic materials that must be treated properly. We must never throw batteries in the batteries in the rubbish. We can also use rechargeable batteries to reduce our energy consumption.

8.3. Positive impact.

Energy efficiency has a beneficial effect on the enviroment.

When we consume less energy, it helps to reduce the greenhouse effect and climate change. It also improves people's health by reducing air and water pollution. Using less energy also reduces our explotation of natural resources.

Renewable energy sources are essential for solving our enviromental problems. In the future, most of the electricity that we use will probably come from these cleaner, greener energy sources.

7. Enviromental impact

Power stations have an important impact on local ecosystems. Power stations also generate waste products taht can affect the environment.

7.1. Environmental impact assessment.

TIPE OF POWER STATION       ENVIROMENTAL IMPACT        ENERGY USED  
        Wind                                          It is non-polluting, but it has                   Renewable
                                                          visual and acoustic impacts.


    Hydroelectric                                It has a major impact because                  Renewable
                                                          it changes the flow of rivers
                                                          and floods large areas.

   
     Solar                                             It is non-polluting, but large                    Renewable
                                                          power stations take up a lot
                                                          of land.


    Marine                                         The construction of marine                        Renewable
                                                         stations affects the local enviroment.


    Biomass                                       The technology is beneficial when it         Renewable
                                                         used properly.


    Fossil fuels                                   Ir pollution contributes to climate              Non-renewable
                                                         change. Water is also polluted when
                                                         it is used for cooling.            


    Nuclear                                        Radiation is very dangerous if there are      Non-renewable
                                                        accidents. The waste products are not
                                                        recyclable.




7.2. Effects on the enviroment.
Energy production includes many steps, from the extraction of natural resources to the transportation and final distribution of energy to consumers. Each of these steps can have an impact on the enviroment.

Extracting natural resources.
Fossil fuels and radioactive elements, such us uranium, must be extracted from underground deposits. When those deposits are exhausted, we must find new ones to replace them.

Transporting fuel.
Most oil transported over land through gas pipelines and by sea in large ships called oil tankers. Natural gas in transported over land through gas pipelines or by sea in tankers as liquid natural gas (LNG). These tankers are called LNG carries. Natural disasters and accidents can also affect gas pipelines and LNG carries.

Generating electricity.
Hydroelectric power stations require large amounts of water which must be stored behind dams in reservoirs. These reservoirs flood large areas of land and change the natural flow of the river. These changes have enormous effects on ecosystems along the entire length of the river.

Waste treatment.
Power stations that use non-renewable sources of energy produce large amounts of waste. However, some steps can be taken to reduce waste and its effects.

• Filters can reduce pollutants, such us nitrous oxide and sulphur.
• Low-sulphur coal can also be used to reduce sulphur emissions.
• Large forests should be protected because they remove CO2 from the air.

Near waste is kept in special conntainers with tick walls that block radiation. These containers are stored in nuclear graveyards, which are usually located underground or in deep ocean trenches.

7.3 Climate change.

Most of our electricity comes from power stations that use non-renewable energy sources. The situation has negative effects on the enviroment, and the most serious is climate change -a problem that is associated specifically with fossil fuels.

• When we burn fossil fuels, gases and methane are released into the air. The gases contribute to the greenhouse effect which increases the Earth's average temperature.
• Already we can observe some of the effects of global warning.
• Power stations that burn fossil fuels also release other pollution into the air. These pollutants combine with water vapour in the air to produce acid rain, which damges our forests.
• These power stations affect plant and animal life because they use refrigeration systems that pump hot water into our rivers and ocean. This increases the local water temperature and also reduces the amount of oxygen in the water.

7.4. Energy consumption.

The fossil fuels that consumers use in their cars on home heating systems also have an affect on the enviroment. In fact, they generate  the same types of air pollution a conventional thermal power stations: CO2, methane, nitrous oxide, sulphur oxide and heavy metals.

6. Power stations that use renewable energy sources.

Some power stations use clean, renewable energy sources to produce electricity. These alternatives help to reduce our dependence on non-renewable sources of energy, such us fossil fuels, which also cause environmental problems.
Renewable energy sources have been developed and improved in recent years. Although these energy sources give us less electricity than thermal power stations, they have several advantages:

• They are 'greener' than conventional power stations because they produce less pollution.
• They use renewable energy, so they don´t consume limited natural resurces.
• They reduce our dependence on other countries that produce fossil fuels. As a result, we don´t need to import so much fuel.
• They are relatively cheap, in comparison to other energy sources.

6.1. Wind farms.
Wind farms use the kinectic energy of the wind to generate electricity. The wind turns the blades of a turbine, at the top of a tower. The blades are connected to a gearbox, wich increases the rotational speed of the generator.



Wind farms are totally clean source of electricity.
The output and efficiency of a wind farm depend on two factos:

• the location of the farm, which determines the speed and strenght of the winds.
• the number of turbines that can be installed there.

6.2. Hydroelectric power stations.

• Conventional hidrolelectric station.

• Pumped storage hydroelectric stations: the water flows from the turbines to a second reservoir.

6.3. Solar power stations.
Solar power stations use energy from sunlight to generate electricity. There are two main types of solar power station: solar thermal and photovoltaic.

• SOLAR THERMAL STATION.

• PHOTOVOLTAIC STATIONS.

6.4.Biomass power stations.

Biomass is any organic material that is produced by natural processes.

There are many types of biomass which ca be used to produce energy. They include natural vegetation, forestry products and agricultural waste. There are also energy crops, such as sunflowers and beets, which are grown specifically for biomass energy production. Biomass is prepared through various physical and chemical natural processes.

In a biomass power station, the fuel used to produce energy comes from biomass. The steam produced from burning the biomass moves a turbine that is connected to a generator.

6.5. Marine power stations.

Marine power stations use the movement of ocean water to generate electricity. At the moment, most of these stations are experimental. They are very expensive and not very efficient. There are three general types of marine power stations.

• Tidal power stations, which use the energy of tides.
• Wave power station, which use the energy of waves.
• Ocean thermal conversion stations, which use the difference in water temperature between the surface of the ocean and deeper areas to produce energy.

6.6. Geothermal power stations.

Use natural heat from the deepest underground layers of our planet. This heat comes to the Earth's surface as hot water, steam and hot gases.

Geothermal energy can be used in two ways:

• It can be directly to provide hot water for heating and industrial uses.
• It can be used indirectly to drive generators and produce electricity.

5. Electric power stations that use non-renewable energy sources

Most of the electricity that we use comes from electric power stations that use non-renewable energy sources. There are two types: thermal power stations and nuclear power stations.

5.1 Thermal power stations that use fossil fuels.
Thermal power stations use fossil fuels to produce thermal energy. Then the thermal energy is converted to mechanical energy, in order to generate electricity.
Fossil fuels which is connected to the rotor of a generator. The generator produces electricity, which is transported by a network of high voltage power lines.

• Combined-cycle power stations.

Is generated in two systems. The first system burns natural gas with compressed air. This produces superhead gases, which turn a turbine to generate electricity.

The second system uses the hot gases from the first system and uses them to produce steam in a heat recovery boiler. Then the steam turns a turbine to generate more electricity. This makes combined-cycle stations more efficient that single-cycle stations.




5.2. Nuclear power stations.

• Advantages: are their productivity and profitability. They produce lots of electricity that can be sold a profit.
• Disadvantages: are the risks of nuclear accidents and the management and storage of radioactive waste.

4. Electrical energy

Electrical energy is a form of energy that is transported by an electrical current.
Electrical energy is the most commonly used energy in modern, industrialised societies. There are many technological objects around us that use electricity.
Electricity is very common for two reasons:

• It can be easily transformed into other types of energy, such us light and heat.
• It can be transported over long distances in ways that are cheap and efficient.

4.1. Electric power stations.
A power station or generating station is a place where energy from natural resources is transformed into energy that we can consume. If the energy obtained is a electricity, it is called an electric power station.

• How electricity is generated.

Electric power stations require sources of energy, such us the mechanical energy of falling water. They use generators used in power stations are called alternators.

An alternator usually has a stationary part, called stator, and a moving part, called a rotor. A turbine turns the axis of the rotor, which generates an alternating electric current in each of the stator's coils, which coincide with one of every two of the rotor's coils.

The turbine-altenator system is used at all power stations except for photovoltaic stations, which use a different type of technology.

4.2. The transportation and distribution of electricity.


The transportation of electrical energy inncludes:

• Raising the voltage.
• High voltage lines.
• Reducing the voltage.

3. Energy sources.

Energy sources are natural resources that we can use to generate different forms energy. Then we can transform that energy for various purposes. We can classify energy sources into two general categories: renewable and non-renewable.

3.1. Non-renewable energy sources.
Non renewable energy sources come from natural resources that are limited and can be exhausted; it would take millions of years o regenerate these sources of energy. At the moment, the most commonly used energy sources are non-renewable. They include fossil fuels and nuclear energy, wich uses radioactive materials.

3.2. Renewable energy sources.
Renewable energy sources come from natural resources that we cannot use up completely. These include hydroelectric, solar, marine, geothermal and biomass resources, as well as energy that we can produce from solid urban waste.

2. Energy transformations.

• A battery contains chemical energy which is transformed into electrical energy (electric current). Then a lightbulb transforms the electrical current into luminous and thermal energy.
• The chemical energy in our muscles can be transformed into mechanical energy in order to move objects.
• Chemical energy can be stored in fireworks. When fireworks explode, that chemical energy is coverted into light, heat, sound and mechanical energy.
• Photovoltaic solar panels tranform luminous energy from the Sun into electrical energy.
• A kitchen mixer converts electrical energy into kinetic energy to turn the machine's axis.
• Internal combustion engines transform the chemical energy of fossil fuels into thermal energy. Most of this thermal energy is transformed into motion, but some is lost as heat. Some energy is also lost as sound when certain parts of the motor hit each other and vibrate.
• In stars, the nuclear energy of atoms, such as hydrogen, is transformed into very intense luminous and thermal energy. 

Energy can be transformed, but it cannot be created or destroyed. This is the principle of energy conservation.

1. Energy.

Foods labels provide us information about the nutritional qualities of the food we eat. For example, the labels on the margin inform us about nutriotional qualities of the milk they go with. Thanks to this data, we can know the energy we'll get if we consume it.

In prehistoric times, muscular energy was the only source of energy that people had. Then different mechanism and machines were invented to make everyday tasks easier and improve people's quality of life.

1.1.Forms of energy.


1.2. Units of measurement for energy.
In the international System (IS), energy is measured in joules (J). When energy takes the form of heat, we often express it as calories (cal).
The relationship between calories and joules is: 1cal = 4.18J.

1.3. Power.
Power (P) is a measurement of how quickly work is done.
The power of a machine is the amount of work that it can do in a certain amount of time. We express this relationships as: P = W/t.
In the previous equation, P is power, expressed in Watts (W); W is work, expressed in joules; and t is time, expressed in seconds (s).

Energy conversion efficiency (%) = output/input · 100

Unit 6: ENERGY

INDEX:       1. Energy

                     2. Energy trasformations

                     3. Energy sources

                     4. Electrical energy

                     5. Electric power stations that use non-renewable energy sources.

                     6. Power stations that use renewable energy sources.

                     7. Enviromental impact.

                     8. How can we save energy?