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12.11.2014
First electric generator
In short, in the presence of an electromagnetic field a current can move a wire and a wire movement can generate a current.
This reversed principle (Faraday's law of induction) was discovered in 1831 by Michael Faraday and as a matter of fact he discovered the operating principle of electromagnetic generators.
Faraday built the first electromagnetic generator, called the Faraday disk, a type of homopolar generator, using a copper disc (instead of the wire) rotating between the poles of a horseshoe magnet.
When the disc was rotated by a handle the apparatus produced a small DC voltage between its hub and rim.
(http://www.juliantrubin.com/bigten/electric_motor_generator.html)
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Picture 3: General layout of electricity network: how the power plants are connected to the electric power grid.
How do light and matter interact when considering generators?
General information about light:
Light interacts with matter in 4 ways: emission, absorption, transmission and reflection or scattering.The interaction between light and matter determines the appearance of everything around us.
Light is a wave of electric and magnetic field where electrons and ions create electric fields. Those electromagnetic waves interact with matter, which contains charges (electrons), and these get pushes and pulled by the oscillating electric field. This motion may absorb or scatter the electromagnetic wave.
Picture 4: How light and matter interact in basic dynamo generator
Solar power
Good example about how light and matter interact in our case is the solar power generator. Solar (or photovoltaic) cells convert the sun’s energy into electricity. Whether they’re adorning your calculator or orbiting our planet on satellites, they rely on the the photoelectric effect: the ability of matter to emit electrons when a light is shone on it.
Silicon is what is known as a semi-conductor, meaning that it shares some of the properties of metals and some of those of an electrical insulator, making it a key ingredient in solar cells. Let’s take a closer look at what happens when the sun shines onto a solar cell.
Sunlight is composed of miniscule particles called photons, which radiate from the sun. As these hit the silicon atoms of the solar cell, they transfer their energy to loose electrons, knocking them clean off the atoms. The photons could be compared to the white ball in a game of pool, which passes on its energy to the coloured balls it strikes.
Freeing up electrons is however only half the work of a solar cell: it then needs to herd these stray electrons into an electric current. This involves creating an electrical imbalance within the cell, which acts a bit like a slope down which the electrons will flow in the same direction.
Creating this imbalance is made possible by the internal organisation of silicon. Silicon atoms are arranged together in a tightly bound structure. By squeezing small quantities of other elements into this structure, two different types of silicon are created: n-type, which has spare electrons, and p-type, which is missing electrons, leaving ‘holes’ in their place.
When these two materials are placed side by side inside a solar cell, the n-type silicon’s spare electrons jump over to fill the gaps in the p-type silicon. This means that the n-type silicon becomes positively charged, and the p-type silicon is negatively charged, creating an electric field across the cell. Because silicon is a semi-conductor, it can act like an insulator, maintaining this imbalance.
As the photons smash the electrons off the silicon atoms, this field drives them along in an orderly manner, providing the electric current to power calculators, satellites and everything in between.
Related subjects
Electromagnetic induction
Faraday’s laws
Photoelectric effect
References
Michael Faraday: The Invention of the Electric Motor and Electric Generator. 2014. Michael Faraday: The Invention of the Electric Motor and Electric Generator. [ONLINE] Available at:http://www.juliantrubin.com/bigten/electric_motor_generator.html. [Accessed 12 November 2014]
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Wind Energy Basics. 2014. Wind Energy Basics. [ONLINE] Available at:http://windeis.anl.gov/guide/basics/. [Accessed 13 November 2014].
photoelectric effect (physics) -- Encyclopedia Britannica. 2014. photoelectric effect (physics) -- Encyclopedia Britannica. [ONLINE] Available at:http://global.britannica.com/EBchecked/topic/457841/photoelectric-effect. [Accessed 03 December 2014].
How do solar cells work?| Explore | physics.org. 2014. How do solar cells work?| Explore | physics.org. [ONLINE] Available at:http://www.physics.org/article-questions.asp?id=51. [Accessed 03 December 2014
Picture 1: http://en.wikipedia.org/wiki/Electric_generator#mediaviewer/File:Generator-model.svg
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http://en.wikipedia.org/wiki/Electrical_grid#mediaviewer/File:Electricity_Grid_Schematic_English.svg
Solar (or photovoltaic) cells convert the sun’s energy into electricity. Whether they’re adorning your calculator or orbiting our planet on satellites, they rely on the the photoelectric effect: the ability of matter to emit electrons when a light is shone on it.
Silicon is what is known as a semi-conductor, meaning that it shares some of the properties of metals and some of those of an electrical insulator, making it a key ingredient in solar cells. Let’s take a closer look at what happens when the sun shines onto a solar cell.
Sunlight is composed of miniscule particles called photons, which radiate from the sun. As these hit the silicon atoms of the solar cell, they transfer their energy to loose electrons, knocking them clean off the atoms. The photons could be compared to the white ball in a game of pool, which passes on its energy to the coloured balls it strikes.
Freeing up electrons is however only half the work of a solar cell: it then needs to herd these stray electrons into an electric current. This involves creating an electrical imbalance within the cell, which acts a bit like a slope down which the electrons will flow in the same direction.
Creating this imbalance is made possible by the internal organisation of silicon. Silicon atoms are arranged together in a tightly bound structure. By squeezing small quantities of other elements into this structure, two different types of silicon are created: n-type, which has spare electrons, and p-type, which is missing electrons, leaving ‘holes’ in their place.
When these two materials are placed side by side inside a solar cell, the n-type silicon’s spare electrons jump over to fill the gaps in the p-type silicon. This means that the n-type silicon becomes positively charged, and the p-type silicon is negatively charged, creating an electric field across the cell. Because silicon is a semi-conductor, it can act like an insulator, maintaining this imbalance.
As the photons smash the electrons off the silicon atoms, this field drives them along in an orderly manner, providing the electric current to power calculators, satellites and everything in between.