4. TYPES OF CURRENT

4.1. Direct current.
Between the terminals of a battery, there is a continuous, stable flow of energy. If we use a voltmeter to measure the current in a car battery, the result will always be 12 volts. This is called direct current.

4.2. Alternating current.
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 0 V and increases to 325 V.
• The current decreases from 325 V to 0 V.
• The current becomes negative and decreases to -325 V.
• The current increases to 0 V.

The variation of any electrical parameter over a period of time is an electric 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.

4.3. 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/√2
4.4. Transformers.
Transformers consist of two windings made of copper wire. If we apply an alternating current to one of them, it will produce a certain voltage in the other. 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

3.1. Series circuit.

Two or more elements form a series circuit when the output of one element provides the input for the next element.
To calculate the total resistance of a circuit, we add the resistance values of each load:
                                                      R = R1 + R2 + R3 +...
One example of this type of connection would be a series of generators.
In other words:                             V = V1 + V2 + V3 +...
 

3.2. Parallel circuit.
If identical batteries are connected in parallel, the voltage of the circuit will not increase.
The equivalent resistance of this type of circuit would be:
                                                    1/R = 1/R1 + 1/R2 + 1/R3 +...
 

3.3. Combination circuit.
A combination circuit has some elements connected in series and other elements connected in parallel.

2. ELECTRICAL 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).
This device has two wires that must be connected in parallel to the element that we are checking.

2.2. Measuring electric current.
Electric current is the charge or number of electrons that flo through the cross-section of a conductor every second.
                                                                  I= Q/t 
Electric current is measured in amperes or amps (A).

2.3. Electric resistance: Ohm's Law.
 The resistance (R) of a material is equal to the voltage divided by the intensity of the 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 has two forms:
 V = R x I    and   I = V/R

2.4. Electric 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 = Vx I x t
Is measured in joules (J).

Electrical power.
The electrical 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 an electrical current flows at a particular tension, we can calculate the power (P) that is consumed:
                                                                        P = V x I
We simply multiply the power in kiloatts by the amount of time in hours.
                                                                        E = P x t

7. ELECTRIC CIRCUITS AND ELECTRONICS

1. AN ELECTRIC CIRCUIT.

An electric circuit is a pathway for the flow of electrons.
Electric current is a continuous flow of electrons through a circuit.

1.1. Parts of an electric circuit.
Electric circuits consist of various parts:

• Generators provide the energy that electrons need in order to move.

 

• Loads are devices that transform electric energy into other types of energy that we can use.

   Light bulbs
  Motors

Resistors
 Bells

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

  Switches
Push buttons
3-Way switches


1.2. Diagrams and symbols.
Generators: electrochemical cell and battery.
Loads: Light bulb or lamp, resistor, motor, bell, relay.
Switching devices: switch, push button, 3-way switch.
Safety elements: fuse.
Measuring instruments: ammeter, voltmeter.
Other parts: connection and bridge.