8 ELECTRONICS

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 indicate by a code of colours and numbers

• Variable resistance or potentiometer

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

• Resistance that dependes on a physical factor

The physical factors that affect resistance may be temperature or the amount of ligtht, for example.

Resistance that depends on temperature is called a thermistor.

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

LDR: resistance thatvaries according to the amount of ligth received. The resistance decreases as the amount of ligth increases.

• Capacitors

Capacitors are componets that can store an electrical charge. The value of a capacitors 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 ligth when an electric current flows through it.

7.ELECTROMAGNETIC CONTROL SYSTEMS

An electromagnetic control systems activates the various parts of a machine, at the rightmoment and for the rigth amount of time, ensuring that the machine funtions properly.

7.1 Cam switch controller

The device on the side of the pulley in the picture above is called a cam. The shape of this deviceallows us to control the moment and duration of an activity, such as the running or the motor or the illumination of a ligth bulb.

7.2 Limit switches

The picture below shows an electrical control system for a water tank. 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.

6.0 (2)ELECTROMAGNETIC MECHANISMS

6.2 Electric Motor
An electric motor is a device that can transform electrical energy into movement. It uses the forces of atracction and repulsion between a magnet and an electricallycharged wire.

6.3 Relays
A relay is an electromagnetic component that works as a switch. When electricity passes through the coil, it acts like a magent. The coil attracts a moveable metal contact towards another fixed contact. When yhe electricity shops flowing, the moveable contact goes back to its original position.