The relationship between matter and electricity

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The relationship between matter and electricity

The atom- By Aditya Abeysinghe

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History of experiments on this relationship

Michael Faraday- Sent electric currents through liquids and presented two laws on electrolysis.

William Crooks and Julius Plucker- Sent electric currents through gases to see the behavior of gaseous atoms on an electric field.

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Cathode raysCathode rays were detected by Sir William Crooks by maintaining a high potential difference between two metal electrodes under a pressure of about 1 Pa. Since the rays were generated from the negative terminal(cathode) and travelled to the anode they were later named as Cathode Rays.

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A typical cathode ray tube is as follows:

- +V High

To vacuum pump

- +

Cathode rays

1 Pa

He

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Experiments done on cathode rays

Many scientist performed experiments to find how the matter present in cathode rays behaved. However much of the valuable results is credited to Sir J.J. Thomson who also discovered the electron. Summary of some of his experiments are as follows:

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1. Cathode rays were sent through an electric and magnetic field separately

Observation: The rays deflected from the cathode towards the positive plate.Conclusion: Cathode rays are negatively charged

V High

To vacuum pump

- +

Cathode rays

1 Pa

He

+

-

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2. A sharp object was kept in the direction where the cathode rays travelled

Observation: Cathode rays formed a similar sharp image on the ray tube in the same directionConclusion: Cathode rays travel in linear paths

Sharp object

Image formed

Cathode rays

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3. A light object was kept on a stand in the direction where rays travelled

Obsevation: The object travelled in the direction of the cathode rays and vice versa when the direction of the rays changed Conclusion: Cathode rays have a kinetic energy and a momentum

Cathode rays- +

Light object

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In addition to these characteristics, cathode rays also have the capability of transparency through materials and a capability of ionizing materials.Thus it is believed that cathode rays consist of a stream of electrons and it emitted radiation.Finally scientists named this radiation as

β radiation

Later Louis de Broglie showed that electrons(stream of cathode rays) act like photons in a dual manner, in that they act both as waves and as particles.

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What actually is an electron?Later experiments on electrons were based on to identify the mass, charge and the mass to charge ratio of electrons.These can be summarized as follows:Scientist Experiment Conclusion

Milikan(Faraday is also credited for finding the charge because he found the charge of a mole of electrons through another experiment)

The oil drop experiment was used to find out the charge of an electron

Electrons had the smallest charge and it was

-1.602×10-19 C

Sir J.J. Thomson Found the charge to mass ratio(e/m ratio)

e/m of an electron=

1.759×1011 C kg-1

_ The mass of an electron was thus calculated using the e/m ratio and the value of the charge

Mass of an electron=

9.108×10-31 kg

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However the charge of an electron was the lowest charge discovered up to date and the mass of the electron is the smallest mass found up to date. Thus the electron is described as the common element that bridges matter with electricity since any charge or mass of any other element can be expressed by means of that of an electron.However, the mass of an electron is less than 1 a.m.u.(atomic mass unit). Therefore the relative mass of an electron is considered zero. Meanwhile the relative charge of an electron is considered as -1.

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Thus an electron can be represented by the following scientific presentation

X = e

0 -1

Relative massRelative charge

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Canal raysIn 1886, Goldstein found that a special type of rays that originated through the anode and travelled towards the cathode. These rays could be best viewed by using a perforated cathode.Similar experiments as that to cathode rays were carried out by Thomson and Mayne

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They found out the following observations:1. The rays deflected towards the negative pole when passed through an electric and magnetic field.(Canal rays are positively charged)2. The e/m ratio depended on the gas inserted. The highest e/m ratio was found when Hydrogen was inserted. (Thus hydrogen was believed to be the lightest of all gases, which now has been confirmed)(Moreover Hydrogen was named as Proton by Rutherford)3. e/m ratio of any other gas was found to be equal to a small-whole-number ratio to that of the hydrogen.(Thus there should be a whole number of protons in any positive atom)

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An explanation of how canal or positive rays are formed is as follows:

Cathode raysAnode/Canal rays

Perforated cathode

Anode

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Important characteristics of Protons

Similar experiments carried out as that for the electron confirmed that

1. Charge of a proton= 1.602×10-19 C

2. Mass of a proton= 1.672× 10-24 g3. The e/m ratio changed according to the

gas used.Moreover the mass of a proton is greater than 1 a.m.u. Therefore, the relative mass of a proton is considered as 1. Charge of a proton equals to that of the electron except the polarity of a + sign. Therefore the relative charge of a proton is considered to be +1

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Atomic models1. J.J. Thompson-

Commonly referred to as the plum pudding model.

According to this model, the atom is made up of electrons, surrounded by a soup of positive charge to balance the electrons’ negative charge.

This is similar to negatively charged plums surrounded by a positively charged pudding

Electrons were free to rotate within the positive substance

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2. Bohr modelConsiders atom as,

small positively charged nucleus, surrounded by electrons travelling around the nucleus in circular orbits.

Electrons can travel from a lower energy state to that of a higher energy state or viceversa.

The difference between any two energy levels is found using the plank’s equation:

ΔE = E (n+1) - En

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3. Rutherford model

Rejected earlier proposed models like the Thompson model.

Electrons are not affected or does not influence the passage of an alpha particle beam

The mass of the atom is mostly centered around the center of the atom (nucleus).

Much of the space occupied by an atom does not constitute most of its constituents

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