- 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