Quantity of electricity
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In physics the term quantity of electricity refers to the quantity of electric charge. It is designated by the letter Q and in the SI system is measured in derived units called coulombs.
[edit] Historical drift
The term quantity of Electricity was once common in scientific publications. It appears frequently in the writings of Franklin, Faraday, Maxwell, Millikan, and JJ Thomson, and was even occasionally used by Einstein.
However, over the last hundred years the term "electricity" has been used by electric utility companies and the general public in a non-scientific way. Today the vast majority of publications no longer refer to electricity as meaning electric charge. Instead they speak of electricity as electromagnetic energy. The definition has drifted even further, and many authors now use the word "electricity" to mean electric current (amperes), energy flow (watts), electrical potential (volts), or electric force. Others refer to any electrical phenomena as kinds of electricity.
These multiple definitions are probably the reason that Quantity of Electricity has fallen into disfavor among scientists. Physics textbooks no longer define Quantity of Electricity or Flow of Electricity. Quantity of electricity is now regarded as an archaic usage, and it has slowly been replaced by the terms charge of electricity, then quantity of electric charge, and today simply charge. Since the term electricity has increasingly become corrupted by contradictions and unscientific definitions, today's experts instead use the term charge to remove any possible confusion.
[edit] Conceptual problems
However, new problems arise when we attempt to fix earlier problems by replacing the term "electricity" with the term "charge." Older scientific papers still exist, and their authors constantly discuss quantities of electricity and flows of electricity (meaning charge and current respectively.) Those historical authors know that their readers understand just one definition: the term electricity means charge and nothing else. Modern students who read physics papers from periods prior to 1930 (approx.) should make a continuous effort to remain aware of this issue. If historical physicists discuss quantities of "electricity" implying "electric charge," yet the modern reader assumes they're speaking of electrical energy, the writings of those physicists will be quite difficult to understand.
Another problem arises because the population of physicists abandoned the term "electricity" without much public discussion and perhaps without much awareness on the part of their community. By silently altering the meaning of common and heavily-used terms, the scientific community caused an immense confusion on the part of the public. Whereas in the past the question "What is electricity?" was more or less easily answered, today the question itself has become meaningless. Is electricity a form of energy? Is electricity the same as electric charge? Is electricity nothing but a class of phenomena, akin to concepts such as "weather" or "politics?" Should we measure the quantity of electricity in coulombs, or should we instead use amperes, joules, or watts, or even volts? Physics texts and reference books supply no solid answer, since physicists have gradually abandoned electricity as a scientific term.
And yet Quantity of Electricity still persists in its original definition in many contemporary references. For example, in the modern SI units of physics, the coulomb is defined both as the unit of electric charge and also the unit quantity of electricity. Encyclopedia Britannica defines the coulomb as the unit quantity of electricity. The Merriam-Webster dictionary, in definition 1a, defines electricity as charge. And until the late 1980s, the glossary in the CRC Handbook of Chemistry and Physics used the term "quantity of electricity" in place of "electric charge" in most of its definitions. Chemistry students will be familiar with Faraday's discovery that a unit quantity of electricity, when passed through an electrolysis cell, liberates a certain number of atoms of metal or gas. Under these definitions, electricity is not a form of energy.
