1. Electricity

  • Electric charge is a property of all objects and is responsible for electrical phenomena.
  • These phenomena are caused by the electrical forces of attraction and repulsion.
  • All matter is composed of atoms. Atoms are made up of other smaller particles:

­                Electrons, which have negative charge.

­                Protons, which have positive charge.

­                Neutrons, which don’t have charge.


1.1.    Electric current

  • Electric current is a continuous movement of electrons. To produce an electric current there must be an imbalance between two points of a conductor. An electric current is a number of electrons that flow through a conductor like water flows through a tube.

­                Conductors are materials that allow electric current to pass through them.

­                Insulators are materials that don’t allow electric current to pass through them.


1.2.    Electric circuits

  • An electric circuit is a set of connected components through which an electric current circulates.
  • Components of an electric circuit:

­              –  Wire conductor. We need a wire conductor to join all the components of an electric circuit.

­              –  Generator: a generator provides the energy necessary to move the electrons.

­              –  Receptors. In a circuit, the receptors are the components that transform electrical energy into another type of energy:

ₒ    Electric resistors produce heat.

ₒ    Bulb produce light.

ₒ    Motors produce motion.

ₒ    Bells produce sound.

­              –  Control and protection components. Control components stop, start or change the direction of the electric current:

ₒ    A switch.

ₒ    A circuit switch

ₒ    A push button.

  • Representation and symbols. A diagram of an electric circuit is a graphic representation using symbols for the components of the circuit.


2. Electric quantities

2.1.    Voltage, current and resistance.

  • The charge is the amount of electricity stored in an object. It is represented by the letter Q and is measured in coulombs (C).
  • Voltage is the difference between the electrical energy at two points in a circuit. It is represented by the letter V and it is measured in volts (V).
  • The current is the number of electrons that pass through a specific point in 1 second. It is represented by the letter I and it is measured in amps (A)
  • Resistance is the opposition of the components of a circuit to the flow of the electric current. It is represented by the letter R and it is measured in Ohms (Ω).

2.2.    Measuring instrument.

  • A voltmeter measures the electrical voltage. You must connect the voltmeter in parallel.
  • An ammeter measures the current. You must connect the ammeter in series.
  • A multimeter (or polymeter) measures different electric quantities on different scales.

2.3.    Ohm’s Law

The proportional relationship between voltage, current and resistance is called Ohm’s Law, and is expressed mathematically as:

V = I x R

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