ELECTRICAL QUANTITIES

1.Voltage or potential difference
The amount of energy that a generator can transfer to electrons depends on its voltage. This is measured in volts (V).
We use a voltmeter to measure voltage. This object must be connected in parallel to the element that we are checking.


2.Intensity or electric current
It is the charge or number of electrons that flow through the cross-section of a conductor every second. It is measured in amperes or amps (A).
We use an ammeter to measure electric current. It must be connected in series.


3.Electrical resistance
The resistance (R) of a material is equal to the voltage divided by the intensity of the electric current wich travels through the material. This is measured in ohms.


4.Electrical energy
It is is the tension that flows, in a certain time, in an electric current. We can calculate it with this formula: E=VxIxt. It is measured in joules (J).


5.Electric power
It is the amount of energy that it can transform over a certain amount of time. It is measured in watts (W) or kilowatts (kW).             P=VxI       E=Pxt




*In the points 1,2 and 3 we can use the Ohm`s Law to calculate it:    R=V/T

AN ELECTRIC CIRCUIT

An electric circuit is a pathway for the flow of electrons, that is called electric current.


-Parts of an electric circuit:

• Generators provide the energy that electrons need in order to move. Examples: cells and batteries.

 

• Loads are devices that transform electrical energy into other types of energy that we can use. Examples: light bulbs, motors, resistors and bells.



• Switching devices are used to direct and interrupt the flow of electric current. Examples: switches, push buttons and 3-way switches.

-Symbols in a diagram:

ELECTRIC POWER STATIONS THAT USE NON-RENEWABLE ENERGY SOURCES

1.Thermal power stations that use fossil fuels
Fossil fuels are used to heat water in a boiler. Steam from the boiler turns a turbine , wich is connected to the rotor of a generator. This produces electricity. After that, the steam goes to a condenser , where it cools and becomes liquid water again, wich is pumped back to the boiler.

2.Nuclear power stations

They work like a termal power station, but this use radioactive materials such as uranium.

-Advantages: productivity and profitability.

-Disadvantages: risks of nuclear accidents and management and storage of radioactive waste.



ELECTRICAL ENERGY

Electrical energy is a form of energy that is transported by an eléctrica current.


Electricity is very common for two reasons:
-It can be easily transformedinto other types of energy.
-It can be transported over long distances.


1.Electric power stations
A power station is a place where energy from natural resources is transformed into energy.
If the energy obtained is electricity, it is called an electric power station.


They use generators (alternators) to transform energy into electricity.

2.The transportation and distribution of electricity

• Raisin the voltage: it is raised to avoid the loss of energy as heat.
• High voltage lines:  are carefully planned and the lines are intalled on towers.
• Reducing the voltage: electrical substations are installed between high voltage lines and final consumers.
• Power is distributed: to homes, offices... The electric lines are usually suported by posts, and the voltage is reduced to very low ranges.

ENERGY SOURCES

Energy sources are natural resources that we can use to generate different forms of energy. Then we can transform that energy for various purposes.


We can classify energy sources into two general categories:

1.Non-renewable energy sources

Come from natural resources that are limited and can be exhausted. They include:

-Fossil fuels (oil, coal ...)

-Nuclear energy (radioactive materials)

2.Renewable energy sources

Come from natural resources that we cannot use up completly. These include: hydroelectric, solar, marine, geotermal and biomass resources.

ENERGY TRANSFORMATIONS

Energy can be transformed, but it cannot be created or destroyed. This is the principle of energy conservation. These are some examples:

ENERGY

Energy is the capacity of a body to perform transformations and do work.

1.Forms of energy:

2.Units of measurement for energy:

In the International System, energy is measured in joules. When energy takes the form of heat, we often express in calories.


3.Power
The power of a machine is the amount of work that it can do in a certain amount of time. We express this relationship as:       P=W/t
The relationship between input and output energy in any machine is expressed as its energy conversion efficiency:           Energy conversion efficiency(%)=(output/input)·100