explanations and experiments

A theory is acceptable while it seems true. When contradictory evidence shows it, or part of it, false it must be modified or scrapped.
At best a theory is an indifferent tool to explain what we cannot comprehend in the first place.
Avoid acceptance of a theory out of sentiment, belief, faith or because someone - who appears important - says you should accept it.


Apparatus used under identical conditions gives identical results to those of someone who did the same experiment elsewhere in space or time. When you repeated Gray`s experiments you got the same results as a man who died 261 years ago in London, England.

Theories arose from observations:- Effluvia - A communicated electric virtue - Fluids, and today - Electrons and ionic activity.

From the 18th through the 19th centuries the Electricians thought their experiments implied the existence of an invisible fluid.

Some textbooks today use hydraulics to explain electrical terms. It is a useful analogy and produced advances in the field of physics.

From experimental results with electrolytes Stoney, in 1874, suggested the existence of a particle he named THE ELECTRON.

In October 1897 J. J. Thomson, investigating discharge through gas, discovered the particle of negative electricity.

This was at a transition point in Natural Philosophy because results from experiments could no longer be explained by existing theory.

Thomson retained Dalton`s idea of solid atoms like billiard balls. His picture was of a lump of positive electricity with negative electrons embedded in it like currants in a bun. There was something comfortable and stable in this idea.

Suddenly, this vanished as Rutherford, in 1911, revealed atoms to be mostly empty space. An atom had a nucleus of positively charged protons around which tiny negative electrons moved in orbits like planets around a sun.

Bohr suggested that electrons moved in fixed orbits. Movement from one orbit to another either involved absorbing or emitting energy. Hence - Quantum theory.

New experimental results showed the electron behaved either as a particle or a wave.

`We can scarcely describe such an entity as a wave or as a particle; perhaps as a compromise we had better call it a `wavicle`.` Eddington - The Nature of the Physical World (1928).
Seventy years on it is
still `such stuff As dreams are made on`. Shakespeare - The Tempest.

It was a good idea but now we need something better.

You may be pleased to learn that we can stay with old Rutherford`s atom for our fun with electricity and magnetism!



Everything in the known world is made from one or more of 92 basic substances called elements.

The smallest piece of an element is called an atom.

Because there are 92 kinds of element there are 92 kinds of atom.

Each element has a symbol - Cu is Copper, O is Oxygen, Ne is Neon and so on.

Each element has an ATOMIC NUMBER.

This informs us of the number of negative (-) electrons and positive (+) protons.

For example, Hydrogen H - Atomic Number 1 - has 1 electron and 1 proton.

Because the negative charge on an electron is exactly matched by the positive charge on a proton an atom is electrically neutral.


A substance may be made of one kind of atom e.g. a piece of gold; or a diamond made of Carbon atoms.

Substances made of combinations of elements are called compounds e.g. water is a compound of Hydrogen (H) and Oxygen (O).

The smallest piece of a compound is a molecule.



Substances are affected by their heat content.

Heat is a form of energy.


At the lowest level of heat energy the substance will be a SOLID. Its structure is a lattice of component atoms called a crystal in which the atoms vibrate but do not move out of position.


Add heat and the atoms vibrate more and more until the crystalline structure begins to break down i.e. the solid melts and becomes a liquid.



Warm a cupful of water.

Stir salt into the water until no more will dissolve.

Pour the salt solution into a flat saucer.

Put it where it is dry.

It may now take days or longer, depending on humidity of the air and temperature, to work.

The water evaporates and leaves crystals of salt.

Examine them through a magnifier.

If you have a microscope put a tiny drop of solution on a glass slide. Watch the edges of it through the microscope to see crystals form.

[Salt (NaCl) is a compound of Sodium (Na) and Chlorine (Cl) atoms.

When you put it in water the molecules came apart - dissolved - into Na atoms and Cl atoms and formed an ionised solution which is called an ELECTROLYTE.

It reached a critical point beyond which no more salt molecules came apart.

As water molecules in the saucer acquired heat energy from the surroundings they escaped from the liquid - became gaseous. The critical point was already in existence so Na and Cl ions had less energy to keep them in solution and they joined together into NaCl - a molecule of salt.

As more water molecules left, so more salt molecules collected, and a crystal began to grow.

The faster the water evaporation the more, but smaller, the salt crystals.]

Crystals are beautiful and have a great aesthetic appeal. The study of crystals is CRYSTALLOGRAPHY.


The atomic components of a liquid are able to move around. In its liquid state a substance will take on the shape of its container and is able to freely change its shape when poured into another container.

Vaporisation - when liquid becomes gas.

Adding heat energy to a substance in its liquid state makes the components move faster. They begin to escape from the surface.


In its gaseous state a substance can take in more heat energy and occupy more space. When confined this is manifested as an increase in pressure.


In the states of Solid, Liquid and Gas, atoms remain intact.

If sufficient energy is added to a gas its atoms break up. This is called ionisation. A plasma is an electrically conducting confusion of detached electrons and protons.


Ionisation is a condition in which some electrons attach to an atom - making it negative OR detach from an atom - making it positive. These `affected` atoms are called ions.



LIQUID TO GAS (vaporisation)

GAS TO PLASMA (ionisation)


PLASMA TO GAS (neutralisation)

GAS TO LIQUID (condensation)

LIQUID TO SOLID (freezing)



Atoms of substances which conduct electricity have electrons, in the outer orbits, which may be detached - by heat energy or electrical repulsion.

These detached electrons are called FREE ELECTRONS.

Imagine free electrons inside a conductor as being similar to a mist of negative charge.

As a whole, a conductor is electrically neutral. The negative mist of free electrons move randomly amongst neutral and positively charged atoms.



In an insulator there are few free electrons to permit electrical conduction. Therefore there is little or no current flow in an insulator. Electric charge either of ions or electrons on the surface of an insulator remain stationary i.e. STATIC ELECTRICITY.


Combinations of insulators and conductors direct electrical charge along paths to undertake some task.

E.g. A copper wire is covered with a plastic insulator.


In the experiment in which electrical conduction was discovered the free electrons went to one end of the conductor - Gray`s rod in the cork and, later, his insulated packthread; similarly in our experiment with a wire.

Charge was detected by the electroscope or a pile of foil or paper bits.

To use electrical conduction, for example, to give us light from a filament, we need to keep the free electrons moving. In other words, to keep them in circulation.

To do this we need to maintain an imbalance of charge so the free electrons can continuously move from negative to positive.

This imbalance can be produced chemically in cells and batteries. Or mechanically by rotating a magnetic field in the vicinity of a conductor in a power station, a portable generator, car alternator or bicycle dynamo.

The free electrons must be able to move away from the imposed negative charge through the conductor, do their work, e.g. heat a lamp filament, and reach the attracting positive charge.

There must be a complete path, A CIRCUIT, along which free electrons can move.

EXPERIMENTAL SUGGESTION - There are hundreds of circuits .

To make a start and get some experience AND stay safe:

use a couple of torch cells to make a battery in a cardboard tube (3 volts).

Use 2.5v or 3 volt bulbs and covered wire.

If you can get lampholders and switches, fine, but you can connect to the bulbs by wrapping wire around the body and fixing a drawing pin in a board for the other connection. Switches can be made by opening a paper clip into a long S-shape.


Anchor one wire and the clip at one end with a drawing pin into a board and the other wire under a drawing pin so that when you press down the long S it makes contact.

You can try bulbs one after the other in a series circuit; OR alongside each other in a parallel circuit; and in series parallel.

With the battery connected and switch on remove various bulbs to see if the circuit is broken and so stops the flow of free electrons.


Connect one wire from a bulb to one terminal of the battery.

Connect a wire to the other terminal of the battery.

Connect a wire to the other side of the bulb.

As yet the circuit is not complete.

Touch the ends of the two free wires to light the bulb to check that the tester is OK.

You can use it to sort insulators (which do not conduct) from conductors.

Suspect fuses - switch off any power supply then remove the fuse- it can then be checked. Tester bulb stays off = fuse blown.



It is not known how, when a plastic tube is rubbed, charge is generated. Mechanisms have been proposed but it remains an unsettled question.

Surfaces are very complicated structures. Fractal Geometry of Surfaces gives a sense of the mysterious akin to that of the `wavicle`.

But we do know that rubbing a plastic tube with a cloth generates an electric charge with one polarity on the tube and its equal but opposite polarity on the cloth.


A negative tube charge is a surplus of electrons, somehow removed from the cloth.

A positive charge is due to electrons leaving the tube and going to the cloth.

Polarity of charge depends on the materials used for the tube and the cloth.

The movement of free electrons in a conductor helps explain what happens in the experiments.

Let`s look at just one to help you work out the others:-


The tube is an insulator - hence no free electrons - so generated charge stays put.

Tube Negative

Near the electroscope, free electrons in the feather move away from negative on the tube and repel free electrons in the cotton thread into the stand and into the earth.

The electroscope is now positive. So we, now, have a negatively charged tube near to a positively charged feather.

Opposite charges attract so the feather moves to the tube.

Tube Positive

The tube attracts free electrons in the feather, thread, stand and from the earth.

This time the feather is negative.

Opposite charges attract so the negative feather moves to the positive tube.

Electroscope Insulated

The same thing, except no free electrons are conducted into or from the earth. The electroscope becomes positive at one end and negative at the other depending on tube charge polarity.



Faster than your reflexes as I discovered in childhood when I tried to beat an electrified cattle fence.
A thought experiment

Imagine a length of pipe just over 2cm inside diameter. The pipe is full of marbles 2cm diameter. Each marble is touching its neighbour.
A marble represents a free electron. You push a marble into one end of the pipe. All move along the pipe a distance of one marble diameter 2cm and a marble falls out of the other end.
The pipe is 186,000 miles long (it is a thought experiment - forget any practical difficulties). Over the period of a second a marble is pushed into the pipe.

Each marble moves 2cm per second. 186,000 miles away a marble falls from the pipe.

Similarly, free electrons drift at the rate of a few centimetres per second but the electrical effect travels at the speed of light.



The end of the metal rod has a sharp edge. It could be turned to a conical point in fact. A current of free electrons moves towards or away from the charge on the plastic tube.

Charge is concentrated at the sharp end of the rod.

There are always ions in the atmosphere - from local and cosmic radiation.

Ions near the rod are attracted to or repelled from the end by the intense collected charge. (Direction depends on the polarity of ions and rod).

Ions collide with air molecules and a chain reaction of ion production ensues. This ionisation emits electromagnetic radiation. Some of the light you see as a glow or brush discharge. The ultra violet aids more ionisation and the radio frequencies you can hear on a nearby radio.

EXPERIMENT - Radio e/m radiation


Listen to a range of crackles as air is ionised by charge concentrated on the tube.


The ionisation of molecules increases as the number of free electrons increases when the tube charge is increased.

Think of the situation of rubbing the tube and increasing its charge. More and more free electrons are moving away from this increasing charge to the far end of the rod.

(The same is true if the tube is positive and free electrons are moving away from the end of the rod so increasing the positive charge there).

The early stages of ionisation produce glows. As the number of ions increases the glow is brighter and streaks of light appear in it - this is CORONA and BRUSH DISCHARGE (ST. ELMO`S FIRE).

Ions collide with ions and air molecules thus ionising them - the process is called an AVALANCHE.

Free electrons on the move from negative to positive - electrical conduction - is an electric current. Likewise, ions on the move - electrical conduction - is an electric current.

In the corona, conducting pathways of charged ions materialise. Once a conducting path appears other ions will rush to travel along it. The path is more intensely ionised and most of the ions now travel along it This avalanche of ionisation is called a SPARK.

Crackles from sparks are sonic waves produced by heated air.

This gave Gray, Franklin and others the feeling that the greater sparks and crackles of thunderstorms may involve electricity.


I will assume the tube charge is negative.

The free electrons in the wire near the tube concentrate on a bulb electrode as they are repelled by the charge on the tube.

The few ions already in existence in the Neon gas will cross the gap between electrodes - i.e. set up an electric current.

Free electrons on the other electrode are now repelled - down the wire along your skin and into the earth.

Ionisation of gas molecules will increase with current flow. When the molecules of a gas are ionised they emit light.

(The light is characteristic - a fingerprint - of the gas, and spectroscopic analysis enables gases to be identified by their spectral `fingerprints` - in stars for example).

If you, now, assume the tube charge to be positive you can work out that the same process occurs but with electrons moving in the opposite direction.


If you have worked as far as this you have gained a lot by your own efforts.

From now on when you come across things electrical you will have a good idea as to what is happening. Congratulations!!!

There are lots of books to take you on from here and to start putting some numbers on it.

My aims are to get you started or explain a few things to you who are already on the way.