Ohms Law - Voltage and Current relationship

Ohm's Law - Voltage and Current relationship Ohms Law is a key rule for analyzing electrical circuits, describing the relationship between three key physical quantities: voltage, current, and resistance. It represents that the current is proportional to the voltage across two points, with the constant of proportionality being the resistance. Using Ohms Law The relationship defined by Ohms law is generally expressed in three equivalent forms: I VÂ  /Â  RR V / IV IR with these variables defined across a conductor between two points in the following way: I represents the electrical current, in units of amperes. V represents the voltage measured across the conductor in volts, and R represents the resistance of the conductor in ohms. One way to think of this conceptually is that as a current, I, flows across a resistor (or even across a non-perfect conductor, which has some resistance), R, then the current is losing energy. The energy before it crosses the conductor is therefore going to be higher than the energy after it crosses the conductor, and this difference in electrical is represented in the voltage difference, V, across the conductor. The voltage difference and current between two points can be measured, which means that resistance itself is a derived quantity that cannot be directly measured experimentally. However, when we insert some element into a circuit that has a known resistance value, then you are able to use that resistance along with a measured voltage or current to identify the other unknown quantity. History of Ohms Law German physicist and mathematician Georg Simon Ohm (March 16, 1789 - July 6, 1854 C.E.) conducted research in electricity in 1826 and 1827, publishing the results that came to be known as Ohms Law in 1827. He was able to measure the current with a galvanometer, and tried a couple of different set-ups to establish his voltage difference. The first was a voltaic pile, similar to the original batteries created in 1800 by Alessandro Volta. In looking for a more stable voltage source, he later switched to thermocouples, which create a voltage difference based to a temperature difference. What he actually directly measured was that the current was proportional to the temperature difference between the two electrical junctures, but since the voltage difference was directly related to the temperature, this means that the current was proportional to the voltage difference. In simple terms, if you doubled the temperature difference, you doubled the voltage and also doubled the current. (Assuming, of course, that your thermocouple doesnt melt or something. There are practical limits where this would break down.) Ohm wasnt actually the first to have investigated this sort of relationship, despite publishing first. Previous work by British scientist Henry Cavendish (October 10, 1731 - February 24, 1810 C.E.) in the 1780s had resulted in him making comments in his journals that seemed to indicate the same relationship. Without this being published or otherwise communicated to other scientists of his day, Cavendishs results werent known, leaving the opening for Ohm to make the discovery. Thats why this article isnt entitled Cavendishs Law. These results were later published in 1879 by James Clerk Maxwell, but by that point the credit was already established for Ohm. Other Forms of Ohms Law Another way of representing Ohms Law was developed by Gustav Kirchhoff (of Kirchoffs Laws fame), and takes the form of: J ÏÆ'E where these variables stand for: J represents the current density (or electrical current per unit area of cross section) of the material. This is a vector quantity representing a value in a vector field, meaning it contains both a magnitude and a direction.sigma represents the conductivity of the material, which is dependent upon the physical properties of the individual material. The conductivity is the reciprocal of the resistivity of the material. E represents the electric field at that location. It is also a vector field. The original formulation of Ohms Law is basically an idealized model, which doesnt take into account the individual physical variations within the wires or the electric field moving through it. For most basic circuit applications, this simplification is perfectly fine, but when going into more detail, or working with more precise circuitry elements, it may be important to consider how the current relationship is different within different parts of the material, and thats where this more general version of the equation comes into play.

How to achieve expert status, HR Zone - Emphasis

How to achieve expert status, HR Zone How to achieve expert status, HR Zone Browse the business aisles of any bookshop and youll find an array of how-to titles. Whether youre hiring or firing, theres guaranteed to be a text extolling the latest methods, explains Rob Ashton. It can be tempting to think that these gurus are cut from a different cloth to normal folk. But the reality is that theyve achieved their expert status in large part by putting their thoughts and ideas in writing. Imagine that youve launched a company-wide initiative that will reduce labour turnover by 10 per cent over a six-month period. The managing director has asked you to share your success at the annual conference. But as the big day looms, you decide to let a colleague take the daunting task of speaking at the podium. Your colleague not only presents the project in all its glory, but speaks with such authority that people automatically associate her with being the expert. And youre left with little, if any, public recognition. The moral of the story (aside from always accepting public speaking invitations) is to make sure you own your ideas by getting them down on paper. For example, you could have distributed reports to all the employees in your company to demonstrate that you were the expert in that particular initiative. Cultivating expert status through writing is a smart move. It can lead to promotions, awards and all manner of challenging opportunities. You may not want to be a Sunday Times bestselling author, but you can still gain credibility within the HR world by writing reports, articles, white papers and blogs. So here are five steps to help you write your way to expert status in your organisation and beyond. One Always ask what employees need and want, even if youve been working with them for years. People change, so keep finding out what really makes them tick. Then, consistently take action to develop original HR practices. Dont be afraid to do things differently (provided of course its not just change for changes sake). Two Think beyond the nuts and bolts of your job and ask yourself how your work truly affects the lives of others. And always focus on the needs of your readers before you write any document. Remember, to gain authority in your organisation, you need people to connect with your writing. So be clear about who will read your document, how important it is to them and how interested they are in it. Use this information to help you shape the content. And make sure you speak directly to the reader by using words such as you, we, us and our. Three Give power to the people by including them in your writing. For example, its more effective to write that one in five people are now happier in their jobs than using the term 20 per cent. And use the active voice as much as possible. For example, youve helped to create over 700 new customers this year is far more effective than Over 700 customers have been created this year with your help. Four Write letters to HR magazines to comment on industry stories. Use the SCRAP formula to help structure your letter. The acronym stands for: situation, complication, resolution, action and politeness. Situation Begin by explaining the current situation or particular issue. For example, you may wish to highlight typical grades of the current graduate intake. Complication Introduce the idea that theres a problem. In this case, the problem could be that personnel managers are wasting time interviewing candidates who dont have the required skills, as grades seem to be a poor indicator of ability in the workplace. Resolution State your resolution to the problem. This could be forging links with universities to conduct undergraduate training in core workplace skills. Action Suggest what action the reader can or should take. You might want the reader to carry out your suggestion locally and report back to you. Politeness Finally, end with a polite, but thought-provoking sign-off. Five Cast your net even wider by contributing full-page articles to HR magazines and other business titles. Always send a synopsis of the article to the magazine first. Write an attention-grabbing headline and standfirst (the two lines under the headline). Then write a snappy opening paragraph and a few sentences about what your article will include. If the editor likes your idea, theyll work with you to decide on the exact content. It doesnt matter if youre a director or working your way up through the ranks, now is the time to start positioning yourself as an expert. Your ideas and recommendations are powerful, so take the time to tell people about them and document them effectively.