Download UNIT: ELECTRICITY What are the components of an electrical circuit

UNIT: ELECTRICITY
What are the components of an electrical circuit? What function do these components have?
What symbols do we use for electrical components?
What electrical effects can we utilise?
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1. Electric charge. Let’s Explore Electricity!
Electricity is the most widely used form of energy. Electricity run our fridges, washing machines
and in general, all electrical appliances in the kitchen. Electricity will probably power all future
cars’ motor.
In order to produce electricity you need another form of energy such as mechanical energy,
solar energy, wind energy and so on.
Rub your pen with a cloth then hold it next to some small pieces of paper. You will see that the
pieces of paper are attracted to the pen. The principle of electric charge explains why objects
attract or repel one another.
Electric charge is a property of all objects and is responsible for electrical phenomena
1. These phenomena are caused by the electrical forces of attraction and repulsion
2. All matter is composed of atoms.
The atom:
To understand static electricity, we have to know the atom, how big it is and its structure. In
other words, what is all the stuff around us made of?
All of the atoms are made up of a “nucleus” situated in the middle of each atom. The nucleus
contains two important kinds of tiny particles, called protons and neutrons. Orbiting around
the nucleus are smaller particles called electrons.
- Electrons have negative charge and are responsible for electric
forces and interactions
- Protons have positive charge
- Neutrons don’t have charge
In general, matter is neutral (it doesn’t have an electric charge). This means that the number
of negative charges (electrons) is the same as the number of positive charges (protons)
Electrons orbit in the space surrounding the nucleus. Electrons are attracted to the protons
and repelled by other electrons.
These forces of attraction and repulsion are much stronger than gravitational forces and are
called electrostatic forces.
Two objects with the same charge repel each other.
Two objects with different charge attract each other.
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2. Electric current
In the previous example, after we electrify the pen, the charges are at rest (not moving). They
don’t move through the electrified material. This is called static electricity. However, electrons
can move though certain materials and create an electric current
Electric current is a continuous movement of electrons
So, we can classify the materials in two cases: conductors and insulators
2.a Conductors
Conductors are made up of atoms whose electrons (conduction band) are able to escape from
the atom’s influence. In a metal, some electrons are not stuck (fixed) to any particular atom
and are free to wander (deambular, vagar) in the metal.
Conductors are materials that allow electric current to pass through them
Examples of conductors:
In general, all metals: Gold, Silver, Copper, Aluminium…
2.b Insulators
On the other hand, insulator materials, such as glass, the outermost electron in the atom is
tightly bonded to the nucleus by an electrostatic force. In this case, most electrons are
attached to particular atoms. Almost none are free to wander through the material, and this
prevent the flow of electricity.
Insulators are materials that don’t allow electric current to pass through them
Examples of insulators:
Glass, Porcelain, Ceramic, Plastic, Rubber, Wood
2.c What produces an electric current?
To produce an electric current there must be an imbalance between 2
points of a conductor (there must be a large number of electrons in 1
point and not in the other). The movement of the electrons stops
when the charge is balanced
An electric current is a number of electrons that flow through a conductor like water flows a
tube
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3. Electric circuits
An electric circuit is a set (group of elements that belong together) of connected components
through which an electric current circulates
Components of an electric circuit:
- a generator
- a wire conductor
- a switch (to open and close the
circuit)
- a receptor (a bulb, a motor, a
resistor…)
3.1 Generator:
A generator provides the energy necessary to move the electrons. It produces a continuous
electric current.
Types of generators (4):
- Batteries: which use chemical processes to - Alternators or dynamos: which transform
generate the electric current.
motion into electric current.
- Photovoltaic solar cells: which use energy - Hydrogen cells: which produce energy from
from the sun
oxygen in the air and hydrogen.
A generator has 2 terminals: 1 positive and 1 negative. When the terminals are connected
with a wire conductor, the electrons move through the wire from the negative terminal to the
positive. The electrons move continuously through the circuit, from one terminal to the other.
3.2 Receptors
In a circuit, the receptors are the components that transform electrical energy into another
type of energy. The electrons leave the generator, taking the energy with them and move
round the circuit. On the way, they can find components that use up some of the energy for
certain purposes.
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Examples of receptors:
- Electric resistors produce heat
- Bulbs produce light
- Motors produce motion
- Bells produce sound
3.3 Controls and protection components:
Components used to control and protect an electric circuit:
3.3.a Controls components stop, start or change the direction of the electric current. The most
common are:
- a switch. Has 2 options: one allows the - a push button. Is similar to a switch, but it
current to pass, the other doesn’t
has one position when you press it and then
it returns to a fixed position
3.3.b Protection components: stop the current when it is too strong so that the important
components of the circuit are not damaged. Examples:
a fuse
a magnetothermic switch
4. Representation and symbols. Diagrams
Compare these two circuits:
It is much easier to use symbols to represent circuits. These are the most common symbols:
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A diagram of an electric circuit is a graphic representation
using symbols for the components of the circuit
5. Electric quantities
The basic electric quantities are:
CHARGE, VOLTAGE, CURRENT, RESISTANCE, ELECTRICAL POWER and ELECTRICAL ENERGY
5.1 Voltage, current and resistance
5.1.a The charge is the amount of electricity stored in an object. Is the equivalent of the
volume of water in the upper container in the water circuit:
It is represented by the letter Q and is measured in coulombs (C).
5.1.b The voltage is the difference between the electrical energy at 2 points in a circuit. The
charge always moves from the point where the energy is highest to the lowest point.
Voltage is represented by the letter V and it is measured in volts (V). This is also called
potential difference (p.d.) (or d.p.p.)
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5.1.c The current is the number of electrons that pass through a specific pint in 1 second. It is
represented by the letter I and it is measured in amperes or amps (A)
5.1.d The resistance is the opposition of the components of a circuit to the flow of the electric
current. It is equivalent to an obstacle. It is represented by the letter R and it is measured in
ohms (Ω)
We sometimes use multiples or submultiples of these units of measurement. For example:
Millivolts (mV) for Voltage; milliamperes or milliamps (mA) for Current or Kilohms (kΩ) for
resistance
5.2 Electrical power and electrical energy
Electrical energy can be transformed into light, heat or mechanical energy. The amount of
energy consumed or produced per second is called power (P):
Power in measured in watts (W) and electrical energy in joules (J) or in kWh (kilowatts hours)
RESUM:
Electric quantities
CHARGE
VOLTAGE
CURRENT
RESISTANCE
ELECTRICAL POWER
ELECTRICAL ENERGY
Letter
Q
V
I
R
P
E
Unit
coulombs (C)
volts (V)
amperes or amps (A)
ohms (Ω)
watts (W)
joules (J) or kWh (kilowatts hours)
6. Ohm’s law
What is the relationship between voltage (V), current (I) and resistance (R)?
The proportional relationship between voltage, current and resistance is called Ohm’s law and
is expressed mathematically as:
This shows that current (I) and voltage (V) are directly proportional for any given resistance
Ohm’s law can also be expressed in 2 other ways:
6.1 Uses of Ohm’s law:
If you know the relationship between the 3 basic quantities you can apply them to solve
problems. Here are some examples of how we can use Ohm’s law:
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7. Activities:
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