Uploaded September 2026 | Updated September 2026, 1 week ago
All matter (any thing) is made up of atoms
One of the oldest and simplest of these is the Bohr model. This describes the atom as consisting of a central nucleus containing minute particles called protons and neutrons. Surrounding the nucleus are a number of electrons in various orbits.
The possible presence of neutrons in the nucleus has been ignored, since these particles play no part in the electrical concepts to be described.
The model shown is not drawn to scale, since a proton is approximately 2,000 times more massive than an electron. Due to its relatively large mass, the proton does not play an active part in electrical current flow.
The behaviour of electrons is therefore more important. However, protons and electrons do share one thing in common: they both possess a property known as electric charge. The unit of electric charge is called the coulomb (C). Since charge is considered to be the quantity of electricity, it is given the symbol Q.
An electron and a proton have exactly the same amount of charge. The electron has a negative charge, whereas the proton has a positive charge.
Any atom in its ‘normal’ state is electrically neutral (i.e. it has no net charge). Therefore, in this state, the atom must possess as many orbiting electrons as there are protons in its nucleus.
If one or more of the orbiting electrons can somehow be persuaded to leave the parent atom, then this charge balance is upset. In this case, the atom acquires a net positive charge and is then known as a positive ion.
On the other hand, if ‘extra’ electrons can be made to orbit the nucleus, then the atom acquires a net negative charge. It then becomes a negative ion.
You may now be wondering why the electrons remain in orbit around the nucleus in the first place. This can best be explained by considering an analogy. An electron orbiting the nucleus may be compared to a satellite orbiting the Earth. The satellite remains in orbit due to a balance of forces. The gravitational force of attraction towards the Earth is balanced by the centrifugal effect resulting from the satellite's high velocity. This high velocity means that the satellite has high kinetic energy. If the satellite is required to move into a higher orbit, its motor must be fired to speed it up. This will increase its energy. Indeed, if its velocity is increased sufficiently, it can be made to leave Earth's orbit and travel out into space.
In the case of the electron, there is also a balance of forces involved. Since both electrons and protons have mass, there will be a gravitational force of attraction between them. However, the masses involved are so minute that the gravitational force is negligible. So, what force of attraction applies here?
Remember that electrons and protons are oppositely charged particles, and oppositely charged bodies experience a force of attraction. Compare this to two simple magnets, whereby opposite poles attract and like (the same) poles repel each other. The same rule applies to charged bodies. Thus, it is the balance between the electrostatic force of attraction and the motion of the electron that maintains its orbit.
It may now occur to you to wonder why the nucleus remains intact, since the protons within it are all positively charged particles! Suffice it to say that there is a force within the nucleus, far stronger than the electrostatic repulsion between the protons, that binds the nucleus together.
All materials may be classified into one of three major groups: conductors, insulators, and semiconductors. In simple terms, the group into which a material falls depends on the number of “free” electrons it has. The term “free” refers to electrons that have acquired sufficient energy to leave their orbits around their parent atoms. In general, we can say that conductors have many free electrons, which drift randomly throughout the material. Insulators have very few free electrons (ideally none), while semiconductors fall somewhere between these two extremes.
All matter (any thing) is made up of atoms
One of the oldest and simplest of these is the Bohr model. This describes the atom as consisting of a central nucleus containing minute particles called protons and neutrons. Surrounding the nucleus are a number of electrons in various orbits.
The possible presence of neutrons in the nucleus has been ignored, since these particles play no part in the electrical concepts to be described.
The model shown is not drawn to scale, since a proton is approximately 2,000 times more massive than an electron. Due to its relatively large mass, the proton does not play an active part in electrical current flow.
The behaviour of electrons is therefore more important. However, protons and electrons do share one thing in common: they both possess a property known as electric charge. The unit of electric charge is called the coulomb (C). Since charge is considered to be the quantity of electricity, it is given the symbol Q.
An electron and a proton have exactly the same amount of charge. The electron has a negative charge, whereas the proton has a positive charge.
Any atom in its ‘normal’ state is electrically neutral (i.e. it has no net charge). Therefore, in this state, the atom must possess as many orbiting electrons as there are protons in its nucleus.
If one or more of the orbiting electrons can somehow be persuaded to leave the parent atom, then this charge balance is upset. In this case, the atom acquires a net positive charge and is then known as a positive ion.
On the other hand, if ‘extra’ electrons can be made to orbit the nucleus, then the atom acquires a net negative charge. It then becomes a negative ion.
You may now be wondering why the electrons remain in orbit around the nucleus in the first place. This can best be explained by considering an analogy. An electron orbiting the nucleus may be compared to a satellite orbiting the Earth. The satellite remains in orbit due to a balance of forces. The gravitational force of attraction towards the Earth is balanced by the centrifugal effect resulting from the satellite's high velocity. This high velocity means that the satellite has high kinetic energy. If the satellite is required to move into a higher orbit, its motor must be fired to speed it up. This will increase its energy. Indeed, if its velocity is increased sufficiently, it can be made to leave Earth's orbit and travel out into space.
In the case of the electron, there is also a balance of forces involved. Since both electrons and protons have mass, there will be a gravitational force of attraction between them. However, the masses involved are so minute that the gravitational force is negligible. So, what force of attraction applies here?
Remember that electrons and protons are oppositely charged particles, and oppositely charged bodies experience a force of attraction. Compare this to two simple magnets, whereby opposite poles attract and like (the same) poles repel each other. The same rule applies to charged bodies. Thus, it is the balance between the electrostatic force of attraction and the motion of the electron that maintains its orbit.
It may now occur to you to wonder why the nucleus remains intact, since the protons within it are all positively charged particles! Suffice it to say that there is a force within the nucleus, far stronger than the electrostatic repulsion between the protons, that binds the nucleus together.
All materials may be classified into one of three major groups: conductors, insulators, and semiconductors. In simple terms, the group into which a material falls depends on the number of “free” electrons it has. The term “free” refers to electrons that have acquired sufficient energy to leave their orbits around their parent atoms. In general, we can say that conductors have many free electrons, which drift randomly throughout the material. Insulators have very few free electrons (ideally none), while semiconductors fall somewhere between these two extremes.
