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The electrical Current


The facility to turn it into another type of energy, etc.

 static current We valued the energy sufficiently. A simple experiment to answer it. It only remains without provision during some minutes in your house (if possible at night). We are going to define the first important concept. Electrical current. It is possible to be defined as the electron movement by a driver.

The left the influence of the passage of electrons of the ball to the body of the girl imagines, Ufff.

The Atom, as it imagines in the image, is made up of particles in the nucleus (neutrons and protons) and other that turn on the same (the electrons) electrons “do not go away of the atom” because an attraction between the positive charges and the refusals exists, but moved away, “yes they are able to go away if they find some positive charge close. This process can be shown in the figure of the right

From this point of view we can classify the materials as drivers and insulators, that is to say, if a material has the most peripheral electrons little attracted the nucleus, are called drivers because it is going to allow that the electrons go from an atom to another one (to see previous graph. On the contrary, if the electron is very bound to the nucleus, there will be no free electrons and there will be no electrical current. To this group Insulator is called to him

The gold, silver, the copper, aluminum, the water of faucet…


Rubber, plastic, porcelain, glass.

Type of current are two: a) DC, if the sense in that the s-electrons move always the same b) AC voltage, if the sense is changing movement electrons DCMovement electrons AC voltage

A small activity. Of the following figures, it indicates what of them represents the DC or CC and the AC voltage or CA


(Work of Lucia Tovar 4º THAT Computer science)

The way to produce electricity in an important manner is by means of the alternator (to see following video)


Electrical magnitudes

Within the electrical current we have three magnitudes fundamental to be able to understand it Current intensity: It is defined as the amount of electrons that happen through a driver in the time unit. One is moderate in Amperes

Tension: It is the energy that has each electron so that it can move. Resistance is moderate in volts:  It is the opposition that presents a body to the passage of electrons. One is moderate in Ohms (represented by the Greek letter Ω) circuit seriesWe are going to give something of returns to these concepts. On the one hand we have a generator, that can be a battery, a dynamo or the alternator. These elements are in charge “to create ready electrons to run by the circuit”. The amount of them who leave makes reference to the Intensity. The energy that takes each makes reference to the Tension and the Obstacles that are going away to find by the way (since they leave until they arrive at the generator) is going to be the Resistance To the right, we have a generator (it pounds) that causes that the electrons leave with certain energy (positive pole) but that is it spending when happening through the light bulbs until they arrive exhausted (without energy) at the negative pole. We can be asked Exist does a relation between the electrons that leave the battery and the resistance (number of light bulbs)? There Ohm with its law comes to solve this enigma of the form


I = V/R




I am the Intensity and it is moderate in Amperes V is the tension and it is moderate in Volts and R is the resistance that there is in the circuit and it is moderate in Ohms

Activity 1º: If we have a battery of 10 volts connected to a light bulb of which it has a resistance of 20 Ω, to calculate the Intensity that leaves the battery.  Solutions

 Activity 2º: If we have a battery of 10 volts with two light bulbs of 20 Ω each, as superior is in the image, to calculate the Intensity that leaves the battery. In this case, it illuminates the light bulbs more or less. The answer reasons. Solution

3º Calcular the resistance of a toaster of 220 volts if the current is of 4 A


Law of the currents of Kirchhoff It is necessary to say that it is more difficult to learn the name that the own law, we see  In a knot where several drivers come together, the currents who enter are equal to the currents that leave This means that if a point of contact enters 20 Amperes, they must leave 20 Amperes. We see some examplesexercise of currents   current problems

Activities. To calculate the value of the current in the following circuits and of saying if it enters or it leaves the currents


Electric power  

circuit series and parallelThe power as the Energy is defined that is developed by time unit, that is P = E/t. The power is a parameter that is used much in the world of the electricity because what comes to say it is the “powerful thing that it is equipment” That means. It is just as they leave few electrons a generator with rather energy that many with much energy. That is the idea. To multiply the Current intensity by the Energy of each to arrive at the Power, therefore defines the Electric power as the product of the Current intensity by the Tension, that is P = V * I If the intensity is moderate in Amperes and the tension in Volts, the Power is moderate in Watts (w). Activities: 4º If a plate of 220 Volts takes from the network 10 Amperes, to calculate the power of the same 5º If we have a light bulb that has a resistance of 20 Ω and it is connected to a tension of 220 volts, to calculate the power 6º a 50 TV of W is connected 10 hours to the day. To calculate the Energy in KWh and the price that we phelp by the same to the month if each KWh costs 20 pennies


Circuits Series and Parallels

  3 light bulbs in series  

If we have two light bulbs, of whichever ways you can connect them. Then, if we connected them a terminal behind another one is called series and if they are connected both would be in parallel. The figure of the left we have two circuits. First it corresponds to a circuit ________and the second to one in ___________   We think a little that happens to him to an electron in each circuit. We begin by the Circuit Series using the electrical Symbolism. The following circuit we have a battery of 9 volts and three equal light bulbs. We can draw the following conclusions

* If they leave 10 electrons the positive pole of the battery,  whatever enter light bulb 1 and whatever leave, whatever enter the 2 and the 3. As we know that the light bulbs do not eat electrons, but only take his energy the answer is that to the salary only a way, the s-electrons always the same, that is that: The Current intensity is always the same in a circuit Series, that is I1 = I2 = I3, being I1 the current of Light bulb 1, I2 the one of Light bulb 2… * If an electron leaves with an energy equivalent to 9 volts and must pass the three light bulbs,  that will happen with its energy if the light bulbs use to give it light. The logical thing is that is losing its energy as pass the light bulbs and therefore the sum of the voltage drop in each light bulb is equal to the tension in the battery, this is 9 V = V1 + V2 + V3, being V1 the tension in Light bulb 1, V2 the tension in Light bulb 2, etc

3 light bulbs in parallel

Now we go with the Parallel Circuit


To the Left a circuit of three light bulbs in parallel (To fix to you again that now the light bulbs illuminate more. Because) We reasoned again * We suppose that they leave 30 electrons the Positive of the battery, by where they are going to happen,  by the B1, the B2, the B3?  if in addition its destiny is the negative of the battery. As the three ways are equal, they are distributed, that is 10 by each light bulb, we arrived at that the intensity that leaves the battery is equal to the sum of the current months in each light bulb, that is It = I1 + I2 + I3 * the energy that has each electron exclusively spends it in one of the light bulbs, because it enters with 9 and it leaves with = volts. This happens to him to each electron and therefore, we arrived at that the tension in a circuit in parallel is always the same, this is V1 = V2 = V3. In the case of the previous circuit V1 = V2 = V3 =) volts


Association of Resistance

 Since we have seen before, the resistance can be connected in series or in parallel.  We see cases both using the symbolism of the resistance. It is possible to be demonstrated that formulate-resistance-seriesassociation of resistance in parallel

a ) If the resistance are in series, the total resistance from the home in the end comes given by the formula: formulate-resistance-parallel

b) If the resistance are in parallel, the Resistance from the home in the end comes given by:

problem resistance 1

Activities. We are going to represent the resistance as they are in fact, not by symbolism). Not to pay attention to the colors.  

parallel7º Calcular the equivalent resistance if R1 = 300 Ω, R2 = 400 Ω and R3 = 200 Ω  


 mixed circuit8º In the circuit of the left, if we connected the resistance in parallel with the same values that before,  that value has the resistance total?

exercise 4 9º Now we have a mixed circuit. If each of them is worth 100 Ω, that value has the total. The following problems we will use the appropriate symbolism.

10 º In this exercise of 3 resistance in series,

a ) To calculate the total resistance

mixed circuit 2


   b ) To calculate the current that leaves the battery

 11 º In the mixed circuit, to calculate a) the equivalent resistance

 b) The Current that leaves the battery

c) The current that circulates around the branch superior and the inferior


Devices to control the Electricity

interrupting symbol They are elements that allow us to block the passage of the current or redirigirlo by another way. We see one by one  

square switch

interrupotor handle


Pulsers1º Interrupting. He is simplest of all. We have it all in the electric appliances to ignite or to extinguish them. It is defined as a device that permanently opens or closes the passage of the current. A great variety of them exists.  In the images of above we can appreciate several types 


2º Pulser. He does just like the switch but is necessary to be pressing the mechanism constantly so that he opens or closes the circuit (according to the type). The symbol is appraised that in 1º case always is open until is pressed. In 2º case always is closed until it is pressed commutatorCommutators.






They are devices that make pass the current through a Terminal or another one. micro-interrupting-sliding We see two applicationscircuit stairs


a ) Stairs of the houses are used for the circuits. In these circuits, from two points the light of the stairs can be extinguished and be ignited. the dormitory, etc change motor turn 1change motor turn 2        

 relayb) Change of turn of a motor. In this case double one is used one.


4º Relays.  They are used to control great currents by the action of small currents. Made up of a Winding (represented by the green rectangle) and the contacts We are going to see a video where one is as it works

  1. Solutions to the activities:
  2. 0,5 A
  3. 0.25 Amperes. Since the current is smaller (in addition there is less tension in the light bulb), the light bulbs illuminate less.
  4. The value of the resistance is 55 Ω
  5. 2200 W
  6. 2420 W
  7.  3 €
  8. 900 Ω
  9. 92.3 Ω
  10. 233 Ω
  11. Total resistance = 80 Ω. Intensity = 112 mA

 a) Req = 45 Ω. b) It =222 mA c) I1 = I2 = 111 mA


Other problems (For students of 3º) 1º Calcular the equivalent resistance and the current that leaves the battery of 9 Volts. b) To calculate the current that goes by the branch of down.     2º In the circuit of the left we have two branches in parallel with a current meter in the branch superior (Ammeter). This measurer indicates that by that branch for 81.8 mA. Calculate the resistance of the light bulb 3º In circuit 3 we see a group of resistance of 100 Ohms each. To calculate the current that leaves the battery and the equivalent resistance

Design PCB