Electricity is a result of the changes, created in a system and tendency to keep a zero charge within the system. We have discussed conserved quantity in Chapter 1. We mentioned under the heading of subatomic particles that one of conserved quantity is zero charge as there is an equal number of protons and electrons in a closed system (a metal bar, as an example of a closed system) or universe, which is a closed system on a maximum scale.
The distribution of negative and positive charges within the system can be changed with one side becoming more positively charged and the other becoming more negatively charged. In such a situation there is a tendency to bring charges to zero within the system, which will create movement of positively charged particles and negatively charged, one towards each other. As positively charged particles are protons, which are trapped in a nucleus, it will be very difficult for them to move. Electrons, on the other side, particularly ones on the outermost shell around an atom, can move freely. They are therefore the ones which move along the system towards positively charged particles with a final go to create zero charge within a system. The movement of electrons within a system from negative charge to positive charge is called Electric current: a phenomenon that takes place when we have electricity. We can have positive and negative charges within the system and they can remain as such with no possibility to go back to zero charges. This happens in situations where between these charges is a material composed of such atoms or molecules, where electrons cannot move freely. Examples are rubber or plastic, which surround electric wires in sockets. Such material is called an insulator.
Materials which allow free movement of electrons are called conductors. Metals such as copper and iron are good conductors of electricity.
When we discussed type of bonding between atoms to create molecules in Chapter 1, we mentioned two main types of bonding: ionic bonding and covalent bonding. This bonding takes place thanks to the tendency of the outermost shell of an atom to have a maximum number of electrons (8 for every next shell apart from the first shell which is 2). In this process only, therefore, electrons on the outermost shell take part in bonding. These electrons are called the valence electrons.
In addition to ionic bonds, specific to metal reacting with nonmetal, and covalent bonds, specific to nonmetal bonds, there is a bond within metal atoms similar to covalent bond, called metallic bonding.
Unlike typical covalent bonding where electrons are shared among two or more atoms within a molecule, in metallic bonding, each atom of metal donates its valence electrons to an electron pool, called a sea of electron, which can freely move across whole material or systems (metallic bar, or iron bar). This is a reason that metals are a good conductor of electricity.
Static electricity is created from excess charge. Within the system we do have an equal amount of positive and negative charges and that cannot be changed. What we can do, however, is to move these charges around and, by doing so, create imbalance in charges in a particular system. As we stated earlier, we cannot move positive charges as they are part of the atomic nucleus, but we can move electrons.
If we use a glass rod and rub it with silk for a while, then a number of electrons from the silk will jump on the glass rod. The rod will become negatively charged, as it will have a surplus of negative charges.
We said that within the system, charge is zero. The glass rod is a closed system. However, charge can be changed in a system if it is not closed and influenced by another system from outside (silk). The glass rod now tends to regain zero charges and in contact with a ping-pong ball will pass these electrons on the ball, making it become negatively charged.
We have the opportunity to experience static electricity in everyday life. On a day after combing hair it can happen that our hair goes up with separation of hair. This happens as a number of electrons pass from comb to hair. As electrons repulse each other, each hair tends to go away from the others. As soon as we touch a material where surplus of electrons from our hair can be passed to, we bring charge of hair to zero, making hair going down take the position it had before becoming charged.
We have already mentioned electric current which is created when electrons move through electric wire.
Historically, although there is some evidence suggesting that people were familiar with static electricity, there was not a significant curiosity for these phenomena before the 17th century. Thales of Miletus has experimented with static electricity in about the 6th century BC, but first experiments with electricity started in the 17th century. Otto van Guericke, German physicist, invented in 1663 the first electric generator. It produced static electricity by applying friction against a rotated ball of sulfur.
Stephen Gray, a British chemist, discovered in 1729 that electricity could flow. Scientists believed during the 18th and the beginning of the 19th century that electricity was a kind of fluid. In 1973, Charles Francois de Cisternay DuFay, a French chemist, divided this fluid in ‘vitreus’ (glass from Latin) or positive and ‘resinous’ or negative electricity. Pieter van Musschenbroek, a physicist and mathematician, first managed to store an amount of electric charge in a device called the Leyden jar. Independently, the same was managed by E. Georg von Kleist, German administrator and cleric. In 1752, Benjamin Franklin, an American printer and publisher, author, inventor and scientist, proved that lightning is an example of electric conduction. Charles-Augustin de Coulomb, French physicist, established a mathematical equation reflecting law in electricity. Luigi Galvani, an Italian scientist, experimented with electricity on animals. With further work in that field by Alessandro Volta, a physicist from Italy, it was constructed first battery as a source of continuous current. It was called voltaic pile. That was invented around 1800. There were many more very great minds who made significant contributions to progress of mankind in that field. I would lose my direction if I were to go into depth in this history. Perhaps to mention only one more name: it is Henry Cavendish, the greatest experimental and theoretical English chemist, who did calculation of density of the earth with precision within 1 % of the currently accepted figure. He experimented with electricity, establishing that its intensity is inversely proportional to distance. A famous laboratory for physics was named in his honour as the Cavendish Laboratory where Joseph John Thomson discovered an electron. There was also a neutron discovered by James Chadwick. Robert Rutherford also started his work at the Cavendish Laboratory. In 1871, James Clerk Maxwell was elected as the first professor of the Cavendish. The laboratory was not completed until 1874.
Magnetism is a phenomenon which is the result of the motion of electric charges either through a conductor such as an electric wire or through space such as the movement of electrons in orbit around an atomic nucleus. In such situations where electric charges are on the move, they produce a magnetic field, which is perpendicular (at the angle of 90 degrees) to the direction of the charge movement.
If we have an electrical current going through wire then a magnetic field is created perpendicular to the direction of the charge in the wire going in a circle around the wire (Picture 2.04). If we put the thumb of the right hand in the direction of the current in the wire and wrap the fingers around the wire, they will point out the direction in which the magnetic field will go (Picture 2.05).
Picture 2.04
Picture 2.05
The magnetic field is always marked as B field while an electric field is always marked as E field. An electric field goes in a direction from positive to negative charges. A magnetic field goes from North to the South Pole of its field. In the case of a simple single straight electric wire with an electric current and magnetic field circling around the wire, it is difficult to define and know where on this circle is North and where is the South Pole. If we, however, make a circle of the electric wire and switch electric current to go through such a circle, a magnetic field will be created where it is easier to locate the North and South Pole. Making a coil of wire long and shaped as a pip
e (this is called solenoid) makes en electromagnet. Here such a pipe of coiled wire is wrapped around a long piece of iron. When electric current is switched through a solenoid then an electromagnet is created (Picture 2.06).
Picture 2.06
If we wrap the fingers of our left hand around the solenoid in the direction of the current of the circled wire, and make a thumbs-up sign, then the stretched thumb will show the location of the North Pole (Picture 2.07).
This is important as if the electrons in the circled wire change their direction then the location of the poles will change their sides as well. For example, if the electrons in the circled wire go clockwise, the North Pole will be up and South down. If electrons go anticlockwise then South will be up and North down (Picture 2.08). This is important in order to have a rough idea about magnetism.
Picture 2.07 Picture 2.08
We know that in our world permanent magnets exists. This refers to a magnet which is already made as such by nature or to a material, which can be magnetised to become a permanent magnet. This kind of matter has a ferromagnetic property. Such a magnet has its magnetic field, which can affect another matter by attracting them. These materials, which can be attracted by magnets, are called paramagnetic. These materials can align their atoms and attach to the magnet but cannot maintain magnetic property and when they are away from the magnet and its magnetic field they do not act as a magnet and cannot attract to each other.
Why do some elements have magnetic properties while others do not?
The answer is in the structure of an atom. Every atom has electrons orbiting around it. Every such electron creates a magnetic field by circling in its orbit around an atom. However, each orbit around an atom can have only 2 electrons; otherwise, the Pauli exclusion principle will be broken. The main point is that these 2 electrons circling around an atom do that in the opposite direction to each other: one circle clockwise and another in an anticlockwise direction. By doing so, one creates the North Pole at the location where the other will create the South Pole. This means that the magnetic field created by these 2 electrons will cancel each other out (Picture 2.09).
Picture 2.09
Therefore, all those elements whose atom is made of a pair of electrons orbiting in each of his orbitals will not express its own magnetic field. If, however, there is only one electron in orbital or one electron in orbitals then the magnetic field of an atom will not be completely cancelled out. What location of North or South Pole of this particular atom will be, will depend on the rotation of the electron whose magnetic field is not cancelled out. In material with paramagnetic property, all atoms in this material have their random position. As each atom has a different position, the direction of their north magnetic fields is in all directions. As a result, we do not have a magnetic property of this material as a whole. However, when we bring this material in a magnetic field of a magnet, then all its atoms align in a direction south-north, reaching magnetic property, and start behaving as a magnet. Once a magnet is removed, their atoms again go to a random position with a subsequent loss of magnetic properties.
With iron, which has a ferromagnetic property, the structure of such material is divided into so-called domains. Each domain within the structure of iron material is aligned, expressing a strong magnetic field. However, each domain is differently aligned to each other so as a whole they cancel each other. Once this structure is brought in a magnetic field of a strong magnet, then each domain is aligned with a magnetic field. They tend to remain aligned so, after the magnet is removed, they remain a magnetic property or become a permanent magnet.
Just to mention that it is not only the circular movement of electrons in orbitals that create a magnetic field in atom but also the rotation of the electron around its own axes, so-called intrinsic spin. Such spin also has protons and neutrons in the nucleus and also creates a magnetic field. This is only for information and I will avoid going into this in detail.
An electromagnet is an example of a nonpermanent magnet, which is switched on when an electric current is switched on and switched off with switching off an electric current.
The history of magnetism dates from the time when a type of rock containing magnetite mineral was discovered. The structure of this mineral is a compound of iron and oxygen written as a chemical formula Fe3O4. It was found in Magnesia, the southeastern area of Thessaly in Central Greece. That is how it gets its name.
It was Thales of Miletus who first experimented with magnetism in around the 6th century BC. Around the same time, Indian surgeon Sushruta Samhita used magnetism in surgery.
In China around the 12th century, the Chinese used a lodestone compass for navigation. (A metal which has a magnetic property is called lodestone.)
The first significant progress in understanding magnetism was made in around 1600 thanks to William Gilbert, a physician and a personal doctor to Queen Elizabeth I. He was the first scientist to discover and state that Earth itself is a big magnet. With continued progress in this field and a number of discoveries and significant work done by many very important people in this field, the pinnacle of achievement was made by work done by James Clerk Maxwell. He basically unified magnetism and electricity, demonstrating that an oscillating current produces an electric field parallel to the direction of the current but also the change of current produces a magnetic field which is perpendicular to the direction of the current and electric field. Both electric fields, manifested as wave, and magnetic field as magnetic wave (both perpendicular to each other) propagate through the space perpendicular to the direction of propagation (Picture 2.10).
Picture 2.10
Maxwell further established that they travel at the speed of light and that electromagnetic waves are, in fact, what light is made of. It depends on their wavelength which part of the spectrum of electromagnetic waves they will be represented with. For example, if the wavelength of electromagnetic waves is in range from 10, 100 or 1000 metres then they will be represented as radio waves or, better to say, expressed and perceived as radio waves. If their wavelength is at the centimetre scale they form or are called microwaves, which are usually in a wavelength of around 12 centimetres. If it is less than a millimetre or just below a micrometre, the electromagnetic radiation is called infrared, which is emitted by objects close to room temperature.
Light is electromagnetic radiation with wavelength between 0.4 to 0.7 micrometres. (Micrometre is a million times smaller than a metre of 1 x 10 on power of –6). Smaller than that, and up to 10 nanometres, we have ultraviolet radiation. Below 10 nanometres to 1/100 of a nanometre, they are called x-rays. With wavelengths below 1/100 of a nanometre, they are called gamma rays as the most powerful electromagnetic radiation with very small wavelengths and high frequency making them electromagnetic waves with very high energy and therefore the most powerful. Picture 2.11 shows radiation from the largest to the smallest wavelength.
Picture 2.11
STRONG FUNDAMENTAL INTERACTION
Strong fundamental interaction presents the most powerful force in nature. Its effects are limited within the range of the atomic nucleus or to be more precise within the size of protons and neutrons. These are interactions between quarks, which keep quarks together within protons (2 up and 1 down quark) and neutrons (2 down and 1up quark). They are so strong within the radius of proton or neutron that they cross boundaries of protons and neutrons. This residual strong force or spillover is called nuclear force, which keeps protons and neutrons together in an atomic nucleus. Their range of dominance is within the distance, which roughly matches the length of 2 and a half diameter of portion. This is as far as spillover or residual force of strong nuclear interaction is concerned. It is important to make this clear distinction between strong nuclear interaction which acts between quarks in baryons (portions and neutrons) and its leftover or spillover called residual strong force or nuclear force.
The force carrier of strong nuclear inter
action is gluon. It is exchange particle, which is located within hadron or baryon and acts as an exchange particle only between quarks. In order to get a rough idea or a slight understanding of this fundamental interaction, we should compare it with electromagnetic fundamental force or gravitational force. In electromagnetic fundamental interaction as well as gravitational one, the strength of these interactions or forces depends on the quantity of charges, positive or negative and mass quantity respectively. In case of electromagnetic forces or interaction, it is a photon, which serves as a carrier of this force, which is neutral.
In the case of strong nuclear interaction, its strength originates in a property called colour. This has nothing to do with original colour but it has some analogy to colour in the sense of a colour mixture and aim to get net of zero colour. What does that mean?
Well, in case of electromagnetic force and imbalance of charge will create electromagnet force moving an electron towards positive charges with a final aim to achieve zero charges. Such behaviours between positive and negative particulars are mediated by photons, particles that exchange this information telling positive and negative particles to rush towards each other. The final result will be zero charges. However, in electromagnetic forces we have only two kinds of charges or particles, positive and negative.
In strong fundamental interactions, which act on quacks in baryons, we have present 3 quarks or 3 particles. Each quark has its own colour, which could be either red, blue or green. These colours are interchangeable among 3 quarks within a baryon. It is not important how many times they change colours among themselves within a proton or neutron. What is important is that at any given time we have 1 quark, which is red, 1 which is blue, and 1 which is green within a baryon. It is important to always have this combination of colour within a baryon as the combination of red + blue +green gives zero net colour. This is in analogy to normal colours. We know that normal clours are part of the light spectrum which itself does not have colour or it could be referred to as a white colour. In essence, light itself can be defined as a zero net colour. We can do an experiment by making a paper circle and painting this circle 1/3 red, 1/3 blue and 1/3 green. We can then attach the centre of that circle to a pan and then start rotating the circle quickly around its own centre. In this situation, red, blue and green colours are not seen any more as separate colours. Instead, they will fuse into one colour, which will be white. We will have then zero net colours.
Journey Through Time Page 6
