|
Post Office Box (electricity)
The post office box was a Wheatstone bridge–style testing device with pegs and spring arms to close electrical circuits and measure properties of the circuit under test. Resistance measurement The boxes were used in the United Kingdom by engineers from then General Post Office, who were responsible for UK telecommunications to trace electrical faults, i.e. to determine where a break occurred in a cable which could be several miles in length. It works on the principle of Wheatstone bridge to identify the resistance of wire connected and then by using wire resistivity and cross section calculating length of wire and thus determining where the cable had broken. Post office boxes were common pieces of scientific apparatus in the UK O-Level and A-Level schools public examination physics syllabus in the 1960s. Construction A typical post office box is in a wooden box with a hinged lid and a metal or bakelite panel showing circuit connections. Coils of wire are wound non-inductive ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Post Office Box (electricity)Tokyo Denki University
A post office box (commonly abbreviated as P.O. box, or also known as a postal box) is a uniquely addressable lockable box located on the premises of a post office. In some regions, particularly in Africa, there is no door-to-door delivery of mail; for example, in Kenya. Consequently, renting a PO box has traditionally been the only way to receive mail in such countries. Generally, post office boxes are rented from the post office either by individuals or by businesses on a basis ranging from monthly to annual, and the cost of rent varies depending on the box size. Central business district (CBD) PO boxes are usually more expensive than rural PO boxes. In the United States, the rental rate used to be uniform across the country. Now, however, a postal facility can be in any of seven fee groups by location; in addition, certain customers qualify for free box rental, usually because the Postal Service does not offer carrier-route delivery to their physical addresses. In the U ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wheatstone Bridge
A Wheatstone bridge is an electrical circuit used to measure an unknown electrical resistance by balancing two legs of a bridge circuit, one leg of which includes the unknown component. The primary benefit of the circuit is its ability to provide extremely accurate measurements (in contrast with something like a simple voltage divider). Its operation is similar to the original potentiometer. The Wheatstone bridge was invented by Samuel Hunter Christie (sometimes spelled "Christy") in 1833 and improved and popularized by Sir Charles Wheatstone in 1843. One of the Wheatstone bridge's initial uses was for soil analysis and comparison."The Genesis of the Wheatstone Bridge" by Stig Ekelof discusses Christie's and Wheatstone's contributions, and why the bridge carries Wheatstone's name. Published in "Engineering Science and Education Journal", volume 10, no 1, February 2001, pages 37–40. Operation In the figure, is the fixed, yet unknown, resistance to be measured. and are ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
University Of Leeds
, mottoeng = And knowledge will be increased , established = 1831 – Leeds School of Medicine1874 – Yorkshire College of Science1884 - Yorkshire College1887 – affiliated to the federal Victoria University1904 – University of Leeds , type = Public , endowment = £90.5 million , budget = £751.7 million , chancellor = Jane Francis , vice_chancellor = Simone Buitendijk , students = () , undergrad = () , postgrad = () , city = Leeds , province = West Yorkshire , country = England , campus = Urban, suburban , free_label = Newspaper , free = The Gryphon , colours = , website www.leeds.ac.uk, logo = Leeds University logo.svg , logo_size = 250 , administrative_staff = 9,200 , coor = , affiliations = The University of Leeds is a public research university in Leeds, West Yorkshire, England. It was established in 1874 as the Yorkshire College of Science. In 1884 it merged with the Leeds School of Medicine (established 1831) and was rena ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
General Post Office
The General Post Office (GPO) was the state mail, postal system and telecommunications carrier of the United Kingdom until 1969. Before the Acts of Union 1707, it was the postal system of the Kingdom of England, established by Charles II of England, Charles II in 1660. Similar General Post Office (other), General Post Offices were established across the British Empire. In 1969 the GPO was abolished and the assets transferred to Post Office Ltd#History, The Post Office, changing it from a Department of State to a statutory corporation. In 1980, the telecommunications and postal sides were split prior to BT Group, British Telecommunications' conversion into a totally separate publicly owned corporation the following year as a result of the British Telecommunications Act 1981. For the more recent history of the postal system in the United Kingdom, see the articles Royal Mail and Post Office Ltd. Originally, the GPO was a state monopoly covering the dispatch of items from ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
O-Level
The O-Level (Ordinary Level) is a subject-based qualification conferred as part of the General Certificate of Education. It was introduced in place of the School Certificate in 1951 as part of an educational reform alongside the more in-depth and academically rigorous A-Level (Advanced Level) in England, Wales and Northern Ireland. Those three jurisdictions replaced O-Level gradually with General Certificate of Secondary Education (GCSE) completely by 1988 and, the International General Certificate of Secondary Education (IGCSE) over time. The Scottish equivalent was the O-grade (replaced by the Standard Grade). The AO-Level (Alternative Ordinary Level) was formerly available in most subject areas. Sometimes incorrectly known as the Advanced Ordinary Level, the AO Level syllabus and examination both assumed a higher degree of maturity on the part of candidates, and employed teaching methods more commonly associated with A-Level study. The AO Level was discontinued, with fina ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Advanced Level In The United Kingdom
The A-Level (Advanced Level) is a subject-based qualification conferred as part of the General Certificate of Education, as well as a school leaving qualification offered by Education in the United Kingdom, the educational bodies in the United Kingdom and Education in the Crown dependencies, the educational authorities of British Crown dependencies to students completing secondary or pre-university education. They were introduced in England and Wales in 1951 to replace the Higher School Certificate (England and Wales), Higher School Certificate. A number of Commonwealth of Nations, Commonwealth countries have developed qualifications with the same name as and a similar format to the British A Levels. Obtaining an A Level, or equivalent qualifications, is generally required across the board for university entrance, with universities granting offers based on grades achieved. Particularly in Singapore, its Singapore-Cambridge GCE Advanced Level, A level examinations have been regar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Physics
Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge which relates to the order of nature, or, in other words, to the regular succession of events." Physics is one of the most fundamental scientific disciplines, with its main goal being to understand how the universe behaves. "Physics is one of the most fundamental of the sciences. Scientists of all disciplines use the ideas of physics, including chemists who study the structure of molecules, paleontologists who try to reconstruct how dinosaurs walked, and climatologists who study how human activities affect the atmosphere and oceans. Physics is also the foundation of all engineering and technology. No engineer could design a flat-screen TV, an interplanetary spacecraft, or even a better mousetrap without first understanding the basic laws of physics ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bakelite
Polyoxybenzylmethylenglycolanhydride, better known as Bakelite ( ), is a thermosetting phenol formaldehyde resin, formed from a condensation reaction of phenol with formaldehyde. The first plastic made from synthetic components, it was developed by Leo Baekeland in Yonkers, New York in 1907, and patented on December 7, 1909 (). Because of its electrical nonconductivity and heat-resistant properties, it became a great commercial success. It was used in electrical insulators, radio and telephone casings, and such diverse products as kitchenware, jewelry, pipe stems, children's toys, and firearms. The " retro" appeal of old Bakelite products has made them collectible. The creation of a synthetic plastic was revolutionary for the chemical industry, which at the time made most of its income from cloth dyes and explosives. Bakelite's commercial success inspired the industry to develop other synthetic plastics. In recognition of its significance as the world's first commercial ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electrical Meters
Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by Maxwell's equations. Various common phenomena are related to electricity, including lightning, static electricity, electric heating, electric discharges and many others. The presence of an electric charge, which can be either positive or negative, produces an electric field. The movement of electric charges is an electric current and produces a magnetic field. When a charge is placed in a location with a non-zero electric field, a force will act on it. The magnitude of this force is given by Coulomb's law. If the charge moves, the electric field would be doing work on the electric charge. Thus we can speak of electric potential at a certain point in space, which is equal to the work done by an external agent in carrying a unit of positi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electronic Test Equipment
Electronic test equipment is used to create signals and capture responses from electronic devices under test (DUTs). In this way, the proper operation of the DUT can be proven or faults in the device can be traced. Use of electronic test equipment is essential to any serious work on electronics systems. Practical electronics engineering and assembly requires the use of many different kinds of electronic test equipment ranging from the very simple and inexpensive (such as a test light consisting of just a light bulb and a test lead) to extremely complex and sophisticated such as automatic test equipment (ATE). ATE often includes many of these instruments in real and simulated forms. Generally, more advanced test gear is necessary when developing circuits and systems than is needed when doing production testing or when troubleshooting existing production units in the field. Types of test equipment Basic equipment The following items are used for basic measurement of voltages, c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Historical Scientific Instruments
History (derived ) is the systematic study and the documentation of the human activity. The time period of event before the invention of writing systems is considered prehistory. "History" is an umbrella term comprising past events as well as the memory, discovery, collection, organization, presentation, and interpretation of these events. Historians seek knowledge of the past using historical sources such as written documents, oral accounts, art and material artifacts, and ecological markers. History is not complete and still has debatable mysteries. History is also an academic discipline which uses narrative to describe, examine, question, and analyze past events, and investigate their patterns of cause and effect. Historians often debate which narrative best explains an event, as well as the significance of different causes and effects. Historians also debate the nature of history as an end in itself, as well as its usefulness to give perspective on the problems o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
_(2).JPG "Click for more on -> Advanced Level In The United Kingdom")
.jpg "Click for more on -> Historical Scientific Instruments")