About 1660, a massive advance made the systematic investigation of electricity possible. It was the electrostatic generator. Invented by Otto von Guerick, it consisted of a globe of sulphur rotating on an axis and was charged by friction.
He was able to show the globe could attract a wide range of objects, and he also observed electrostatic repulsion. Objects attracted to the globe often repelled each other.
Stephen Cray in the seventeenth and eighteenth centuries first introduced the ideas of materials being either conductors or insulators. He also discovered that an electrostatic charge could be induced on a body without their being in contact. Soon afterward, Volta built the first battery.
These early investigations were very rudimentary. For electricity and magnetism to be fully understood, mathematical tools – vectors and calculus  and new physical ideas – fields and potential – needed to be introduced.
]]>It is common to make measurements relative to the 'fixed stars'. These are stars so distant that they appear to be fixed in the sky, apart from their nightly and seasonal motion as the Earth tilts on it's axis, while always rotating about the pole star.
The motion continues during the day, but the light from the stars is trivial compared to the light from the Sun, so is not visible. The Sun however, rises in the East and sets in the west, also rotating about the pole star, rising higher in summer and lowest in winter.
]]>He showed that this interaction existed, and that the wires exerted forces on each other. Parallel – or like  currents attract and antiparallel – or unlike  currents repel.
In addition there exists a simple formula expressing the force between the wires. It is proportional to each current separately, so also to their product and inversely proportional to the distance between them. We may write
The definition of the unit of current is called Ampere and is derived from the above formula. It is that constant current in each of two infinite, straight, parallel wires of negligible cross section that will produce an attractive force ofnewton per metre of length when placed in a vacuum.
The constant of proportionality is thenIn fact we include constantsand a 2 to give
In addition Ampere also derived a useful relationship between the integral of the magetic field around a closed loop and the current passing through the loop, which is very useful in cases where there is a lot of smmetry, allowing the magentic field to be easily calculated.
]]>The apparent motion of Mars as seen from the Earth is shown below,
As Earth and Mars move from positions 1 to 2, 2 to 3 and so on topositions 5 Mars appears to move from A to B then backwards from B toC to D thence forwards again to E.
The model also explained why Mercury and Venus appear close to theSun, but there were small differences which at that time could not beexplained, due to the fact that the orbits of the planets were notcirclesm but ellipses. To account for these differences Copernicusadded epicycles, which Kepler later made unnecessary by modelling theorbits as ellipses.
]]>He also described the natural motion of bodies in the following way:
heavier things fall faster, with speed being proportional to weight.
The speed with which a body falls is inversely proportional to the density to the medium it is falling through.
From the second statement he concluded a vacuum to be impossible, since it would have zero density, implying an infinite speed of descent.
For violent motion, he stated the the speed of an object to be proportional to the applied force. If you stop pushing an object it should stop moving. Though correct for many situations, especially where friction is involved, it does not explain projectile motion, which is a smooth curve.
Aristotle explained projectile motion in terms of a combination of violent and natural motion. When the violent motion 'runs out', the natural motion takes over and the stone falls to the ground.
]]>He also proposed a 'one fluid model' of electricity, with electricity consisting of positive and negative charges. This allowed him to explain the phenomenon of static electricity. If two objects are rubbed together and one is made to hold a positive charge, then the other must be negative charge. In his own language, electric fluid is transferred from one object to another. Today we see static electricity as arising from an exhange of electrons.
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Bohr Model 
Schrodinger Model 

Assumptions 
The angular momentum of electrons in the atom occurs (is quantized) in integral multiples ofwhere Planck's constant 
The electron is assumed to be a wave. Quantization arises naturally as a whole number of wavelengths needs to fit in a single orbit. 
Ease of Use 
Quite simple to understand and use. 
The maths is very difficult and the model is much harder to understand. Higher level maths is required. 
Limitations 
Unable to explain fine structure in the energy levels, and can not be applied to heavy atoms – atoms with more than one electron. 
Model works in principle for all atoms, though for heavy atoms, the solutions are found numerically with the aid of computers. This is primary due to the electrons acting as waves interfering with each other. 
Successes 
Predicts the principle energy levels with accuracy. 
Predicts all hydrogen energy levels accurately. 
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Light exists simultaneously as a wave, with wave properties – wavelength, frequency, able to undergo reflection, interference, diffraction – and particle properties – localisation, having momentum and capable of undergoing collisions with other particles, obeying the principles of conservation of momentum and energy.
De Broglie's contribution to quantum physics was to generalise the light model as a wave particle synthesis to all particles. If light, which most people supposed to be a wave, could exhibit particle properties, then maybe matter particles could exhibit wave properties. The relationship between the wave and matter properties of particles and light appears in the form of an equation
where= the momentum of the particle (or light photon)
= Planck's constant
= wavelength
In fact all particles and waves exist as wavepackets that label the position of the particle.
The waves that constitute the wavepacket interfere constructively towards the centre of the wavepacket but less so towards the edge, and exhibit complete destructive interference outside the wavepacket.
Wave particle duality generalises to ordinary things – tables chairs etc but the momentum of these ordinary things is so large that the wavelength is very small and we think of them as ordinary matter.
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