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It is this difference in charge that makes the grains move even in the absence of wind.

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The wind erodes the earth's surface causing the friction that generates the electrostatic charge, negative in the grains and positive in the ground.

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A study by the University of Michigan shows the presence of electric charges in the deserts capable of carrying sand particles and arranging them tadily.

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To comb the sand of great deserts are not only the movements of the air, there is also an electric force.

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Dunes and valleys in the deserts seem softly designed and always perfectly smooth.
But how is it possible?
Why doesn't the wind mess them up?
How do they become more and more regular?

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Electricity... linked to a grain of sand!

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Electricity... linked to a grain of sand!

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Meanwhile, a single falling drop, whose path was recorded, captured the emitted electrons.

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The law is not totally due to Coulomb, given that the same experiments of Coulomb were previously conducted by  Henry Cavendish, who for his bizarre personality did not publish most of his work. However, this was the first attempt to understand how electric force works.

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- Positive charges move towards the land.
-Thunders are attracted by the lightning rod, invented by B. Franklin, and they go to the ground, without causing any damage.

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Farmers' Almanac - Plan Your Day. Grow Your Life.

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Plan ahead with the Farmers' Almanac. See the best days to plant, fish, and more! Long-range weather forecasts, full Moon dates, and gardening tips-as well as bits of folklore that spark conversation. Plan ahead with our calendars. See the best days to plant, fish, and more!

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Human body is a conductor!

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if we touch the sphere, the electrons fall on the ground and the sphere becomes only positive charged (no more neutral).

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As a consequence, there is an attraction-->INDUCTION

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Since the ebonite rod is negatively charged, there is a separation between opposite charges in the metal sphere --> POLARIZATION

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VALENCE ELECTRONS: they are free to move

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The metal sphere is a CONDUCTOR.

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The electric force between two charges at rest is directly proportional to the charges themselves and inversely proportional to the square of the distance.

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The charge assumed by every drop was always a multiple of −1,602 × 10−19 C, now officially considered the electron's charge.

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He radiated the environment with x-rays which caused the expulsion of electrons from the atoms of the air.

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Millikan inserted small drops of oil between two placed that could be electrically charged

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The tool isn’t able to give a quantitative description of the charge, but only a qualitative description.

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In reality the positive charges cannot move and everything happens because the electrons move from the bottom to the top.

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The leaves are charged with the same sign and repel each other. The greater the electric charge, the greater the amplitude of the angle formed by the two golden leaves.

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If the disc is touched with an electrified object (for example, a pen rubbed on the wool), part of the charge passes through the auction by electrostatic induction and so the charge is distributed throughout the device, up to the leaves.

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It consists of a vertical metal rod, with a conductive sphere at the top and two very thin conductive leaves at the bottom. Everything is enclosed in a glass container.

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Consequently, the positive charge (and therefore the mass) of the atom is concentrated in a point, the nucleus, around which there is an empty space that allows the passage of the radiation, in this space, the electrons orbit around the nucleus.

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Just a few alpha particles, which are positively charged, are rejected by the positive charge of the gold atoms; the greater part, however, is only deviated or is able to pass undisturbed.

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The results were as follows:

-          A large part of the particles crossed the plate without deviating;

-          Some particles were deviated from the initial direction of angles called “angles of diffusion”

-          Just a few particles bounced back with extreme violence.

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After having determined the nature of α radiatons (helium atoms deprived oftwo electrons), Rutherford used them to bombard the gold atoms of a very thin lamina (0,01 mm); after the impact, the particles were collected by a special screen able to detect them.

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It establishes that, for a linear dynamic system, the effect of a sum of input perturbations is equal to the sum of the effects produced by each individual perturbation.

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              THE SUPERPOSITION PRINCIPLE

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              THE SUPERPOSITION PRINCIPLE

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The positive charge of the molecules determines a negative layer around them, that effectively reduces the strenght of Coulomb’s force.

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Each molecule is an induced dipole.

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Inside the molecule, the charge is separated--> induced electric dipole

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The electrons are pushed away by the negative charge of the pen, so they move on the further side of the molecule, so the closer side becomes positively charged.

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The baloon (neutral) is attracted by the pen; the reason is in the molecular structure of the baloon itself.

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The baloon (neutral) is attracted by the pen à the reason is in the molecular structure of the baloon itself .

The electrons are pushed away by the negative charge of the pen, so they move on the further side of the molecule, so the closer side becomes positively charged.

Inside the molecule, the charge is separatedà it induced an electric dipole

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It’s similar to induction, but refers to insulators rather than metals (conductors), and the scale is different.

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It explains two phenomena:
1. When we rub a pen it becomes polarised
2. When Coulomb’s force is reduced in matter

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A too high concentration of charges leads to a discharge.

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2)      Van de Graff generator (1929)

Tool: empty metal sphere linked with a rubber belt, which is in contact with a metal brush;

- brush A is linked to a positive generator; the belt is charged by friction and electrons flow towards the generator, while the positive charge moves (carried by the belt) and is transferred to the sphere by a second brush B

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                               ELECTROSTATIC GENERATORS

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                               ELECTROSTATIC GENERATORS

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In 1993 Chadwick discovered another nuclear particle, the neutron, having mass but not charge; since attractive forces are not possible, neutrons and protons stick together thanks to a new force, the nuclear force.

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1) positive α rays (helium nucleus)

2) negative β rays (high-speed electrons)

3) neutral γ rays (photons)

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During his research, trying to explain the phosphorescence of some uranium crystals, he put a photographic plate in contact with the crystals and realized that the plate had been impressed even if it had not been exposed to sunlight.
The material emitted rays without the need for and excitation by the light: RADIOACTIVITY

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The scientist noticed that a screen strewn with platinoapnide of uranium and placed near the tube glinted slightly. In an attempt to discover the origin of the rays, he placed his hand in the trajectory and noticed that the shadow of the bones could be seen right behind (first radiography ever).

The rays, called “x” as unknown, arose from the contact between the cathode rays and the anticathode.

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Crookes used a pump capable of producing the vacuum inside a glass tube connected to two plates, the electrodes, a positive one called “anode” and a negative one called “cathode”. When the gas pressure inside the tube was a millionth of atmosphere, a fluorescent spot was observed in front of the cathode: the cathode emitted rays (the so called "cathodic rays") which propagated in straight line.

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Atomic model: the pudding.

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Conclusion: if the rays’ parts are smaller than the atom, atoms can be divided; in addition, since they are generally neutral, atoms also contain a positive charge.

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- The rays coming out of the cathode are NEGATIVE (in fact, they are deflected nearby a positive object)

- The ratio e/m (charge to mass) is really big, consequenty mass is minute

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John Joseph Thomson - cathode ray tube 1897

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John Joseph Thomson - cathode ray tube 1897

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Non-metals (like plastic) are insulators

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Metals are conductors

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If glass is used, the force becomes attractive; so there are two types of electricity:

-resineous (repulsive)

-vitreous (attractive)

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1)      The first rod approaches to the other, but nothing happens

2)      The rod is electrified and the observer witnesses the development of a repulsion force (which remains the same with amber, rubber, ebonite, wax, wood)

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1)      Volta’s electrophorus (1775)

The tool consist of two parts:

-a fixed dielectric plate (resinous material)

-a mobile metal plate with a dielectric hardle

The dielectric plate is negatively charged; when it is put in contact with the metal plate, the metal plate undergoes induction

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-Egyptians knew about electricity

- Thales of Miletus discovered the properties of amber, which attracts little bodies if it is brushed with hair

-William Gilbert stated that wax and wood have the same property of amber, introducing the name of “electricity” (elektron, in ancient greek, means “amber”)