Basics of Electricity and Magnetism

A Story of Symmer`s Stockings

In the mid-eighteenth century, the Reverend Robert Symmer followed fashion and wore silk stockings. In November 1758 the weather was cold so he took the precaution of first putting on a pair of dark woollen stockings over which he pulled on his silk stockings.

On returning home he sat on his bed and pulled off his stockings and noticed to his amazement they flew away from each other. So began his experiments into electricity. He found the woollen stockings would be attracted to the silk ones; that woollen stockings pushed each other away and so did the silk ones and on very cold nights the stockings seemed to still have a leg inside them.

At first he thought the colour of the material may be responsible for their electrical properties but abandoned that idea. He decided that the material from which the stockings were made somehow governed their electrical behaviour.

Symmer reasoned that the woollen stockings had one kind of electricity and the silk another. He proposed the hypothesis that the two kinds of electricity exist in all things. It is sometimes possible to draw off a quantity of one kind and so leave a surfeit of the other and that electrical phenomena resulted from this imbalance of what he called the electrical `fluids`.

This is called a two fluid theory of electricity.

I will not outline all the theories proposed to account for electrical phenomena - but I can recommend reading up on the history to gain an insight both into experimentation, apparatus design and, at times, frantic activity to explain observed phenomena.

Out of all this enthusiasm, fun, name-calling, claim and counter claim, came the basics listed below and once you have these you are well on the way to understanding most of what goes on in natural phenomena, your own electrical experiences and applications of electrical knowledge.

ELECTRICITY - Like Charges Repel. In other words:- a negatively charged object will try to push away another negatively charged object. Similarly a positively charged object will push away another positively charged object.

Unlike Charges Attract. A positively charged object and a negatively charged object will pull on each other.

Insulators - are materials which oppose the flow of an electric current. If a charge is generated on an insulator - for example if you rub a piece of PVC with a woollen cloth - the electric charge stays put on the plastic. It is STATIC - stationary - stays put. The study of charges on insulators is called ELECTROSTATICS. The early experimenters called insulators ELECTRICS. Examples are dry wood, dry glass, amber, rubber, most plastics.

Conductors - are materials which permit the flow of an electric current. If you rub a length of metal, say a piece of copper pipe, no charge can be detected. We now know the reason is that as the charge is produced it flows away through the pipe, through your body and into the earth.

Gray et al had immense problems with this phenomena. It seemed at the time that electricity could be produced on ELECTRICS, that is, on INSULATORS but not on what they called NON-ELECTRICS (that is CONDUCTORS). It was a major discovery to find if a NON-ELECTRIC is not in contact with the person or the earth then it will behave like an ELECTRIC (an INSULATOR) and hold a static charge. DUFAY following on the researches of Stephen Gray demonstrated this by placing the material he was rubbing on a glass support. Examples of CONDUCTORS are - most metals, salt water or any water containing ions, living plants.

SEMICONDUCTORS - these days our lives have undergone dramatic changes due to materials which are insulators which can be made to conduct. Since I am dealing with the basics of e & m I will not be including semiconductors here - essentially speaking if you get the idea of insulators, conductors and the basics then semiconductors are as it were the next stage.

MAGNETISM - LIKE POLES REPEL. The North pole of any magnet will push away the North pole of any other magnet. Likewise the South pole of any magnet will push away the South pole of any other magnet.

UNLIKE POLES ATTRACT. The North pole of a magnet will pull to it the South pole of any other magnet and vice versa.

Notice the similarity to the behaviour of electric charges. Also, it seems that although you can have individual polarities of electric charge, say all negative; you cannot have an individual magnetic pole - if there is a South pole then somewhere not too far away is its attendant North pole.


An electric current flowing through a conductor produces a magnetic field around the conductor.

A magnetic field moving where there is a conductor will produce an electric current in the conductor.


Some Natural Phenomena

CAVES - The radioactive decay of radium into radon daughters in the clays and rocks of caves and mines results in the air being ionised - made electrically conducting. The presence of an atmospheric Low (Pressure) has the effect of releasing more gas. The ionised air rises upwards from the cave or mine entrance. This constitutes a natural lightning conductor . It is dangerous to shelter in a cave or mine entrance during a thunderstorm. A lightning discharge may well travel down the column of conducting air rising from the cave or mine.

Waterfall Electricity - LENARD discovered that the spray around waterfalls is charged with electricity. This is most likely due to the shattering of water droplets - a process known to generate electricity in thunderclouds and sea spray.

Sea Spray - Each time a bubble bursts in water an upwardly moving WORTHINGTON jet is produced. This jet of water breaks up into a number of droplets, the smallest being at the tip of the jet. In the case of sea water these tiny droplets are electrically charged and evaporate to form beautiful crystalline structures. BLANCHARD estimated some 3,000 million tons of salt per annum are released into the earth`s atmosphere by bursting bubbles.

Thunderstorms - There are some 1200 thunderstorms per hour in the earth`s atmosphere. The storm cloud is called a CUMULO-NIMBUS and has several electrical cells in its structure. The average height of the cloud is 9 miles but some reach up to 15 miles. A cell recharges inside the cloud within 30 seconds after a lightning discharge.

Volcanic Lightning - During eruptions a lightning whose structure seems peculiar to volcanoes is often seen in the ejectamenta cloud. Some lightning is probably due to impacting dust but many volcanoes are submarine, on the rims of oceans or have water in their structure. These are electrically charged by contact of water with hot lava - first demonstrated by D.C. BLANCHARD at the eruption of Surtsey - In later investigations C. POUNDER discovered the mechanism by which electrically charged solute particles are produced.

Dust Storms - The impacts between grains and the separation of grains produces electricity in clouds of dust. In sand storms electric sparks are seen. MILLS demonstrated in a simple experiments how such dust storms may occur on Mars, the lightning in them produces radio noise.

Snow storms - Lightning has been observed in snow blizzards. Andrew Crosse recorded that on a still night with no storms in his neighbourhood the Leyden Battery he used to collect atmospheric electricity began to ring a small bell attached to it. He looked from his windows to see snow falling and concluded it was electrically charged.

Tornado - Inside the whirlwind funnel lightning has been observed flashing across the core. First hand eye-witness of this came from a man who, thinking the tornado has passed over, opened his storm shelter door to find himself looking straight up inside the funnel of the tornado. BERNARD VONNEGUT did some investigative work on this incident - a part of his ongoing many years study of thunderstorms. It is with great sadness, since he was a friend of mine, I have to record the news which came during my writing this that Bernie is dead.

Earthquake Lightning - Japanese scientists in particular are investigating violent, often horizontal, lightning witnessed during earthquakes. One hypothesis is that tons of quartz bearing rock strata are dislocated in the event and the lightning results from piezoelectricity . Another hypothesis is that aqueous solution contact charging (see above on Volcanic Lightning) may be the cause.

Biogenesis - Origin of Life - The amino-acids found in proteins have been synthesised in experiment simulating early conditions on the planet. The first of these by STANLEY MILLER in 1953AD set up a laboratory flask and spark apparatus to model the lightning through the earth`s primitive atmosphere.

Radio Signals from Space - Radio Astronomy was initiated by KARL JANSKI of Bell Telephone Laboratories when he realised interference on long telegraph lines came from the Sun and Jupiter. MILLS as mentioned demonstrated similar noise from dust storms on Mars. The whole science now investigates electrical discharge generated radio signals from discharges in galaxies, stars and planets.

Electric Eels and Fish - Great argument `about it and about` basically along the lines , "Electricity and water don`t mix!" Anyone who had made a fool of himself with his electrostatics demonstrations because his glass machine or Leyden Jars were damp was not keen to even think that the Electric Eel was powered by the sometimes elusive electric charge. Faraday and Cavendish made investigations. Cavendish constructed a model eel from a leather cylinder connected to a charged Leyden battery. Visitors were invited to grasp it and decided for themselves whether electricity was involved.

More recent investigators have lit an electric lamp. Which suggests another reason why we should keep our fingers out of tropical aquaria.

Neurology - The brain and nervous system work by the transmission of electrical signals produced by the interchange of Sodium and Potassium ions through membranes. The basic law that a conductor carrying an electric current is surrounded by a magnetic field leads one to speculate that complex magnetic fields, ever changing, must exist around each one of us - and plants of course.

Bacteria - There are several kinds of bacteria which either synthesise or ingest Magnetite Fe3O4 which enables them to navigate, presumably along the inclination of the earth`s magnetic field, downwards into Oxygen free regions in mud. The flagellea of E-Coli are turned by electric motors employing ion movement. Nano- technology is beginning to copy this ancient electric motor mechanism.

Earth - William Gilbert the earth was a magnet following on from his experiments with a sphere of Magnetite. One hypothesis suggests that the magnetism arises in consequence of large electric currents circulating in the molten Mantle. Whence come the currents one wonders.

Flares on the Sun pour electrically charged ions into the Solar Wind which sweeps the planet`s upper atmosphere. Ionised layers are formed which reflect radio waves and in part shield us from ultraviolet. The ions cause the aurora -Borealis and Australis. Magnetic storms from the wind distort radio signals and induce large currents in power transmission lines.

Plants - Lightning produces nitrous and nitric acid (see Henry Cavendish). These dissolve in water drops which then fall as acid rain. The rain is drawn into the ground by gravity and capillary action and dissolves minerals. This solution of water and ionised minerals is an electrolyte. (An ion is an atom -the smallest part of an element - or a molecule - the smallest part of a compound - which has lost or gained one or more of electrically charged particles. Usually this involves only electrons).

The electrolyte is taken up by the plant roots, in particular by the root hairs. It is converted by various processes, for example Photosynthesis, into cellular material.

Hence lightning produces our food.

A TREE IS A POSSIBLE LIGHTNING CONDUCTOR. Electrically speaking the Cambium of a tree filled with an electrolyte is a vertical conductor. Lightning striking a tree causes the electrolyte to flash into steam and there may be a steam explosion which shatters the tree. If the tree bark is smooth and wet the discharge may pass along this into the ground. Rough bark in part prevents an easy path to ground. In either case however side flashes are common. A tree through which a small electrical discharge passes is subject to cellular damage.

If you are standing next to this vertical conductor when lightning strikes it the electricity will find another easier passage to ground through the vertical conductor of bloodstream and organs and you will suffer cellular damage.

Electrostatic Hazards - Many of the natural manifestations of dust and spray electrification arise in manufacturing processes. Sugar, flour, powdered chocolate and grain silos have all exploded in instances where there has been charging of the dust clouds and subsequent spark discharge. Coal dust explodes due to dust electrification and discharge. The cleaning of tanks on oil supertankers by the use of high pressure water spray led to Waterfall Electricity which produced sparks which ignited resident gases causing death and insurance claims.

Rev. Symmer would not these days be greeted with incredulity and laughter by those who wear man made fibre. In the dark we are often entertained, or scared stiff, by blue corona, brush discharge and crackling sparks. Although the voltage involved is very high the current is extremely low and risk of electrical injury is low. Most injuries occur to limbs when reaction causes a person to hit a limb on the furniture.

In the Court of St. Petersburg there was a game of throwing a fur muff charged up the people taking part and they discharged sparks to the furniture or each other.

Liquid fuel will generate charge so much so that sparks have been seen in petrol passing through a transparent pipe. Tankers and the vehicle receiving fuel need to be well earthed (grounded).

Sellotape flips back to the roll due to electrostatic charging when it is peeled.

Fabric woven in machines in which fibres pass at speed over metal rollers generate high charges which may tangle the threads. Sheet plastic produced over rollers build up high charges which can affect production -and anyone standing nearby. Precautions have to be devised in all these cases to reduce the build up of charge. Sometimes a radioactive source ionises local air to make a conducting path for discharge to take place continuously.

Helicopters may charge to 500,000volts when rotors collide with rain drops or ice particles.

One use of spray electrification is in electrostatic paint spraying in which the charged paint droplets form even coats everywhere on the article to be painted. Another use is in the application of pesticides which attach all over leaves.

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