4)TYPES OF CURRENT

DIRECT CURRENT
Between the terminals of a battery, there is a continuos,stable flow of energy. If we use a volmeter 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 connected a light bulb to a battery, the electrons always flow in the same direction with the same current.
ALTERNATING CURRENT
In alternating current the flow of electrons changes direction 50 times every second,as if the positive and negative poles of the socket were constantly changing places.In addition, the electric current is not always the same.
If we measured the voltage of an electrical socket,the results could be represented in a graph like the one below:

• The current begins at 0V and increases to 325V.
• The current decreases from 325V to 0V.
• The current become negative and decreases to -325V.
• The current increases to 0V.

The variation of any electrical parameter over a period of time is an electrical signal.
The tension or voltage of domestic electricity is an alternating signal because it alternates between positive and negative values.Its waveform is also sinusoidal, with a smooth, regular shape.
Alternating current is produced by generators, such as the ones in large electrical generating stations.There are stations may use conventional source of energy or non-conventional sources.

THE EFFICIENCY OF ALTERNATING CURRENT
The average power of alternating current is equal to the direct current that is needed to produce the same effect.In the case of an alternating sinusoidal current, the average power would be as follows:
                                              Vef=Vmax/Raíz cuadrada de -2
TRANSFORMERS
There is an important difference between alternating and direct current.Alternating current can be increased or decreased by a transformer.This allows us to transfer electrical energy at very high voltages and over hundrers of kilometres,without losing any of the energy as heat.
Transformers consit of two windings made of copper wires.If we apply an alternating current to one of them(V1), it will be produce a certain voltage in other(V2).The value will depend on the number of times that the copper wire has been wrapped around each winding, represented as n1 and n2:
                                    V1/V2=n1/n2

3)TYPES OF CIRCUITS

SERIES CIRCUIT
Two or more elements form a series circuit when 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.
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To calculate the total resistance of a circuit, we add the resistance values of each load:R1+R2
PARALLEL CIRCUIT
In the 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 of each element, but the current that flows through each branch is different.The equivalent resistance of this type of circuit would be:
                                        1/R=1/R1+1/R2+1/R3
If identical batteries are connected in parallel,the voltage of the circuit will not increase. However, the total consumation of energy will be shared between the batteries, so each one will last longer.

COMBINATION CIRCUIT
A combination circuit has some elements connected in series and other elements connected in parallel.

In this type of circuit, the current remains constant between elements that are connected in series.At the same time, the voltage remains constant between elements are connected in parallel.

2)ELECTRICAL QUANTITIES

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ELECTRICAL RESISTANCE: OHM'S LAW
The resistance(R) of a material is equal to the voltage divided by the intensity of electric current which travels through the material. This ratio, which is called Ohm's Law, can be expressed as follows:
                                                         R=V/I
Ohm's law have other two forms:
                                           V=R*I          I=V/R
ELECTRICAL ENERGY AND POWER
Electrical energy
If a electric current(I) flows at a particular tension(V) for a certain amount of time(t), we can calculate the energy (E) that is consumed: E=V*I*t
In the SI, this electrical energy is measured in joules(J).
Electric power
The electric power of a load is the amount of energy that it can transform over a certain amount of time.Electric power is measured in watts(W) or kilowatts(kW).
If a electric current(I) flows at a particular tension(V), we can calculate the power(P) that is consumed:
                                                  P=V*I
The electrical energy that is consumed can be expressed as a function of power and time, using the kilowatt per hour(kW/h) as a unit of measurement.
If we know the power of a load, we can calculate the electrical energy that it consumes over a certain amount of time. We simply multiply the power in kilowatts by the amount of time in hours.
                                                                       E=P*T

2)ELECTRICAL QUANTITIES

VOLTAGES OR POTENTIAL DIFFERENCE

The amount of energy that a generator can be transfer to electrons depends on its voltage(V) or electric tension. This is measured in volts(V).
If we want to meausure the voltage, we can use volmeter. This divice has two wires that must be connected in paralell to the element that we are checking.

MEASURING ELECTRIC CURRENT
Electric current(I) is the change or number of electrons that flow through the cross-section of a conductor every second. We can express this mathematically as flollows:
                                 I=Q/t
Electric current is measured in amperes or amps(A) in the international system.
We can use an ammeter to measure electric current.

1)AN ELECTRIC CIRCUIT

An electric circuit is a pathway for the flow of electrons. If consits of the following parts, which are connected by wires: A generator that provides energy, elements that provide control and protection; loads that receive and use energy.
Electric current is a continous flow of electrons through a circuit.

PARTS OF AN ELECTRIC CIRCUIT

• Generators provide the energy that electrons need ir order to move.
• Loads are devices that transform electrical energy into other types of energy that we can use.

• Switching devices are used to direct and interrupt the flow of electric current.
  

DIAGRAMS AND SYMBOLS

We use a system of conventional symbols to simplify the visual representation of electric and electronic circuits, making them easier to understand.
The following table list the most common symbols:

UNIT 4 ELECTRIC CIRCUITS AND ELECTRONICS

Hello! Today we are going to start a new unit about electric circuits and electronics. In this unit you will learn to:

• Identify basic electrical and electronic components and their symbols.
• Use basic instruments and units of measurements for electricity.
• Design and build simple electric and electronic circuits.
• Draw circuit diagrams using the correct symbols.
• Explain various effects of electric circuit and how it is converted.
• Design and build a model car that is powered and controlled by electrical devices.