ELECTRONIC COMPONENTS

- Resistor.
Opposes the flow of electric currents, which we measure in ohms, is indicated by a code of colours and numbers.

- Variable resistance.

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

- Resistance that depends on a physical factor. 

· Depends on temperature is called a thermistor:

Negative temperature coefficient (NTC): the resistance decreases.

Positive temperature coefficient (PTC): the resistance increases.

· LDR: the resistance varies according to the amount light received. Decreases as the amount of light increases.

- Capacitors.

Are components that can store an electrical change. The value of a capacitor indicates the change volts that it can store. This is measured in farads (F).

- Diodes.

It allows electric current flow in one direction. A diode has two electrodes: an anode (A) and a cathode (K).

A LED only gives off light when an electric current flows through it. Diode symbol:

ELECTROMAGNETIC CONTROL SYSTEMS

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

- Cam swith controller.
The shape of a cam control the moment and duration of an activity, for example, the light of a bulb.

- Limit switches.
The battery provides power for the pump, which moves water from the lower tank to the upper tank. The limit switch is activated when the upper tank is full and the float rises to a certain level.

ELECTROMAGNETIC MECHANISMS

Electromagnetic mechanisms convert movement into electricity or vice versa.

- Electromagnetic generators.
Transform mechacical energy into electricity. There are two types of generators, depending on the type of current that is produced:
· Dynamos: consists of a magnet and a rotary coil. The coil is located between the poles of the magnet. The coil have two semi-circular conductors, which form th conmutator. The electricity applied generate direct current.
· Alternator: is identical to a dynamo, except for the conmutator, which consists of two metallic rings connected to carbon brushes. This produces alternating current.

- Electric motors.
Transform electrical energy into movement. Use forces of attraction and repulsion.

- Relays.
A relay is an electromagnetic component that works as a switch. When the electricity stops flowing, the moveable contact goes back to its original position.

EFFECTS OF ELECTRIC CURRENT

- Heat.
The movement of electrons through an electrical cable is both slow and disorderly, the electrons often collide, increasing the temperature of the cable itself.
The energy that produces as heat is called th Joule Effect: E = I2 x R x t

- Light.
There are various ways that electricity can be used to produce light : 
· Incandescent bulbs: when an electric current passes through the metallic filament of a light bulb, it produces light. This is called incandescence.

· Fluorescent tubes: the electric current passes through the filament, electrons are emitted into the inert gas, these react with the mercury, creating invisible, ultraviolet light.

· Light-emitting diodes (LED): a LED has layers of semiconductor materials. When electricity is applied to the LED, the electrons and holes cross over into the active layer, where they combine produce particles of light.

- Electromagnetic effects.
The scientist Michael Faraday noticed that electricity could be generated by using a magnet and an electrical conductor. This principle allows os to build dynamos and alternators.

- Sound. 
We use bells and buzzers to transform electric current into sound.