8. ELECTRONS

 8.1. Electronic components.
  
Fixed resistance or resistor.

A fixed resistance or resistor opposes the flow of electric currents, Its value, which we measure in ohms, is indicated by a code of colours and numbers.





Variable resistance or ptentiometer.
The value of a variable resistance or potentiometer can be adjusted between zero and the maximum value specified by the manufacturer.





Resistance that depends on a physical factor.
The physical factors that effect resistance may be temperature or the amount of light:
  -Resistance that depends on temperature is called a thermistor. There are two types of thermistors:

• Negative temperature coefficient (NTC) : The resistance decreases as the temperature rises.
• Positive temperature coefficient (PTC) : The resistance increases as the temperature rises.

 -LDR: Resistance that varies according to the amount of light received. The resistance decreases as the amount of light increases.

Capacitors.
A capacitor can store electrical energy from a battery and then use it to power a light bulb until the charge is totally depleted.
Capacitors are components that can store an electrical charge.
The value of a capacitor indicates the charge in volts that it can store. This is measured in farads (F).

Diodes.
A diode is an electronic component made from semiconductor materials. A diode has two electrodes: an anode (A) and a cathode (K).
A LED only gives off light when an electric current flows throught it.

Transistors.
They are made from semiconductor materials and have three electrodes called the base, the collector and the emitter.
There are two types of transistor: NPN and PNP.

• When no electrons are flowing through the base, then no electrons can pass from the collector to the emitter. The transistor is in cut off.
• When many electrons are flowing through the base, the route between the collector and the emitter will be completely open. The transistor is in saturation.
• When the flow of electrons through the base is between the cut off and saturations levels, it will be proportional to th flow of electrons between the collector and the emitter. The transistor is in the active region.

8.2. Basic devices made with eletronic components.
Timers.
A timer is a device that operates for a cetain period of time and then shuuts itself off automatically.
Integrated circuits.
Integrated circuits consist of miniature electronic components, such as transistors, resistors and capacitors.

7. ELECTROMAGNETIC CONTROL SYSTEMS.

7. ELECTROMAGNETIC CONTROL SYSTEMS.

An electromagnetic control system activates the various parts of a machine, at the right moment and for the right amount of time, ensuring that the machine functions properly.

7.1. Cam switch controller.
The device on the side of the pulley in the picture above is called a cam.

7.2. Limit switches.
The battery provides power for the pump, which moves water from the lower tank to the upper tank. When the upper tank is full, a limit switch turns off the pump.

Normally closed (N/C)
It opens when it is activated.

Normally open (N/O)
It closes when it is activated.

6. ELECTROMAGNETIC MECHANISMS.

6. ELECTROMAGNETIC MECHANISMS.

They use electromagnetic phenomena to produce electricity or convert it into mechanical energy.

6.1. Electromagnetic generators.

Generators that produce direct current are called dynamos, and those that produce alternating current are called alternators.

Dynamos.
A dynamo consists of a magnet and a rotary coil. The coil is located beteen the two poles of the magnet. The ends of the coil have two semi-circular conductors, which form the commutator.

Alternators.
A simple alternator is almost identical to a dynamo, except for the commutador, which consist of two metallic rings connected to carbon brushes. Instead of a direct current, this produces alternating current.

6.2. Electric motors.

An electric motor is a device that can transform electrical energy into movement. It uses the forces of attraction and repulsion between a magnet and an electrically-charged wire.

6.3. Relays.
A relay is an electromagnetic component that works as a switch. Relays may have a single circuit with one moveable contact. 

5. EFFECTS OF ELECTRIC CURRENT

5.1. Heat.
The energy that an electric current produces as heat is called the Joule Effect.
It is expressed by the following formula:
                                                E = I^2 x R x t

5.2. Light.
Incandescent bulbs.
When an electric current passes through the metallic filament of a lightbulbs, it produces light. This phenomenon is called incandescence.

Fluorescent tubes.
Inside a fluorescent tube, there is a metallic filament, normally of tungsten. There is also an inert gas, such as argon, and a small amount of mercury.

Light-emitting diodes (LED)
A light-emitting diode (LED) has layers of semiconductor materials.

5.3. Electromagnetic effects.
In this experiment, the electric circuit has created a magnetic field. This effect can be used to produce movement.

5.4. Sound.
We can transform electric current into sound by using electromechanical devices, such as bells and buzzers. Some of these devices are based on the piezoelectric effect.