VOLTAGE CURRENT RESISTANCE POWER /WATTAGE VOLTAGE MOST HOMES ARE120 TO 240 VOLTS.ITS GET MUCH HIGHER IN MANUFACTURING NEXT SOME TIME INCREASE PLS WAIT
Monday, 10 November 2014
CONDUCTOR MATERIALS.INSULTER MATERIAL
CONDUCTOR ALLOW FLOW OF ELECTRICITY. COPPOR.GOLD.SILVER.ALUMINUM.MERCURY.STEEL.BRASS.BRONZE. GRAPHITE.DIRTY WATER.CONCRETE. A CONDUCTOR IS ANYTHING THAT FLOWS THE FLOW OF ELECTRIC CHARGE. INSULTER MATERIAL INSULTER DO NOT NORMALLY ALLOW THE FLOW OF ELECTRICITY GLASS PORCELAIN RUBBER ASPHALT FIBERGLASS CERAMIC QUARTZ DRY COTTON DRY PAPER OIL AN INSULTER IS JUST THE OPPOSITE OF CONDUCTOR
WHAT IS ELECTRIC CIRCUIT
An electrical circuit is a device that uses electricity to perform a
task, such as run a vacuum or power a lamp. The circuit is a closed loop
formed by a power source, wires, a fuse, a load, and a switch.
Electricity flows through the circuit and is delivered to the object it
is powering, such as the vacuum motor or lightbulb, after which the
electricity is sent back to the original source; this return of
electricity enables the circuit to keep the electricity current flowing.
Three types of electrical circuits exist: the series circuit, the parallel circuit,
and the series-parallel circuit; depending on the circuit type, it may
be possible for electricity to continue flowing should a circuit stop
working. Two concepts, Ohm's
Law and source voltage, can affect the amount of electricity flowing
through a circuit, and therefore, how well an electrical circuit
functions.
Electrical engineers are
responsible for managing the ways power flows in business and home
settings. During an interview, several questions will generally revolve
around the candidate's expertise with electrical principles and the
technology associated with it. Interviewers also ask questions regarding
the prospective employee's past success in school and at work. In
addition, interviewers also typical ask about situations where lessons
were learned by the interviewee. Personality also plays a major role in
electrical engineering interview questions because a company is
interested in finding a mindset that fits well with an engineering team.
Technical electrical
engineering interview questions are among the most frequently asked of a
potential employee. Questions regarding Ohm's law, circuit-related
theorems, mutual induction, and the like are frequently asked of anyone
wishing to become an engineer. Complex problems involving electrical
engineering applications are also common during the interview process.
For example, an interviewer could ask about an electrical related
problem and how the interviewee would resolve the issue. These questions
are posed to gauge how quickly a candidate's thought process works and
to also assess the applicant's intelligence and aptitude.
Many interviewers will ask
electrical engineering interview questions that focus on successes in
the electrical engineering field. Usually drawing from experiences in
school and from professional life, the applicant often will be called
upon to talk about projects that concluded with positive results. This
is an opportunity for the candidate to showcase a strong work ethic,
problem solving abilities, and leadership. ELECTRIC ENGINEER INTERVIEW
Electrical engineers are
responsible for managing the ways power flows in business and home
settings. During an interview, several questions will generally revolve
around the candidate's expertise with electrical principles and the
technology associated with it. Interviewers also ask questions regarding
the prospective employee's past success in school and at work. In
addition, interviewers also typical ask about situations where lessons
were learned by the interviewee. Personality also plays a major role in
electrical engineering interview questions because a company is
interested in finding a mindset that fits well with an engineering team.
Technical electrical
engineering interview questions are among the most frequently asked of a
potential employee. Questions regarding Ohm's law, circuit-related
theorems, mutual induction, and the like are frequently asked of anyone
wishing to become an engineer. Complex problems involving electrical
engineering applications are also common during the interview process.
For example, an interviewer could ask about an electrical related
problem and how the interviewee would resolve the issue. These questions
are posed to gauge how quickly a candidate's thought process works and
to also assess the applicant's intelligence and aptitude.
Many interviewers will ask
electrical engineering interview questions that focus on successes in
the electrical engineering field. Usually drawing from experiences in
school and from professional life, the applicant often will be called
upon to talk about projects that concluded with positive results. This
is an opportunity for the candidate to showcase a strong work ethic,
problem solving abilities, and leadership. ELECTRI SHORT CAUSE
An electrical short or a
short circuit is a problem which occurs when an accidental path is
created in a circuit, generating a connection where one did not exist
before. Since electrical current follows the path of least resistance,
it would follow this path rather than the one established in the
circuit, causing an unusually high flow of current. Classically, shorts
occur when bare wires cross, as for example when the insulation in an
old outlet wears away, allowing wires to touch each other. People
sometimes use the term “short” to refer to any problem with an
electrical system, regardless as to whether or not it is a true
electrical short.
Electrical shorts are very
serious problems. The high rate of current results in the generation of
heat, which can cause sparks or a fire. An electrical short often
generates a distinctive popping noise when the circuit is activated, as
the electricity follows the new connection it has discovered and the
circuit is suddenly overloaded with energy. Smoke or flames may appear,
and the short can be strong enough to melt insulation on electrical wiring, or to cause damage to the circuit itself.
Main article: Electric shock
A voltage applied to a human body causes an electric current through
the tissues, and although the relationship is non-linear, the greater
the voltage, the greater the current.[65]
The threshold for perception varies with the supply frequency and with
the path of the current, but is about 0.1 mA to 1 mA for mains-frequency
electricity, though a current as low as a microamp can be detected as
an electrovibration effect under certain conditions.[66] If the current is sufficiently high, it will cause muscle contraction, fibrillation of the heart, and tissue burns.[65]
The lack of any visible sign that a conductor is electrified makes
electricity a particular hazard. The pain caused by an electric shock
can be intense, leading electricity at times to be employed as a method
of torture. Death caused by an electric shock is referred to as electrocution. Electrocution is still the means of judicial execution in some jurisdictions, though its use has become rarer in recent times.[67]Applications
The light bulb, an early application of electricity, operates by Joule heating: the passage of current through resistance generating heat
The Joule heating effect employed in the light bulb also sees more direct use in electric heating. While this is versatile and controllable, it can be seen as wasteful, since most electrical generation has already required the production of heat at a power station.[58] A number of countries, such as Denmark, have issued legislation restricting or banning the use of electric heating in new buildings.[59] Electricity is however a highly practical energy source for refrigeration,[60] with air conditioning representing a growing sector for electricity demand, the effects of which electricity utilities are increasingly obliged to accommodate.[61]
Electricity is used within telecommunications, and indeed the electrical telegraph, demonstrated commercially in 1837 by Cooke and Wheatstone, was one of its earliest applications. With the construction of first intercontinental, and then transatlantic, telegraph systems in the 1860s, electricity had enabled communications in minutes across the globe. Optical fibre and satellite communication have taken a share of the market for communications systems, but electricity can be expected to remain an essential part of the process.
The effects of electromagnetism are most visibly employed in the electric motor, which provides a clean and efficient means of motive power. A stationary motor such as a winch is easily provided with a supply of power, but a motor that moves with its application, such as an electric vehicle, is obliged to either carry along a power source such as a battery, or to collect current from a sliding contact such as a pantograph.
Electronic devices make use of the transistor, perhaps one of the most important inventions of the twentieth century,[62] and a fundamental building block of all modern circuitry. A modern integrated circuit may contain several billion miniaturised transistors in a region only a few centimetres square.[63]
Electricity is also used to fuel public transportation, including electric buses and trains. [64]
ain article: Electricity generation. See also: Electric power transmission and Mains electricity.
Thales' experiments with amber rods were the first studies into the
production of electrical energy. While this method, now known as the triboelectric effect, can lift light objects and generate sparks, it is extremely inefficient.[48]
It was not until the invention of the voltaic pile in the eighteenth
century that a viable source of electricity became available. The
voltaic pile, and its modern descendant, the electrical battery, store energy chemically and make it available on demand in the form of electrical energy.[48]
The battery is a versatile and very common power source which is
ideally suited to many applications, but its energy storage is finite,
and once discharged it must be disposed of or recharged. For large
electrical demands electrical energy must be generated and transmitted
continuously over conductive transmission lines.
Electrical power is usually generated by electro-mechanical generators driven by steam produced from fossil fuel combustion, or the heat released from nuclear reactions; or from other sources such as kinetic energy extracted from wind or flowing water. The modern steam turbine invented by Sir Charles Parsons in 1884 today generates about 80 percent of the electric power in the world using a variety of heat sources. Such generators bear no resemblance to Faraday's homopolar disc generator of 1831, but they still rely on his electromagnetic principle that a conductor linking a changing magnetic field induces a potential difference across its ends.[49] The invention in the late nineteenth century of the transformer meant that electrical power could be transmitted more efficiently at a higher voltage but lower current. Efficient electrical transmission meant in turn that electricity could be generated at centralised power stations, where it benefited from economies of scale, and then be despatched relatively long distances to where it was needed.[50][51]
Since electrical energy cannot easily be stored in quantities large
enough to meet demands on a national scale, at all times exactly as much
must be produced as is required.[50] This requires electricity utilities
to make careful predictions of their electrical loads, and maintain
constant co-ordination with their power stations. A certain amount of
generation must always be held in reserve to cushion an electrical grid against inevitable disturbances and losses.
Demand for electricity grows with great rapidity as a nation modernises and its economy develops. The United States showed a 12% increase in demand during each year of the first three decades of the twentieth century,[52] a rate of growth that is now being experienced by emerging economies such as those of India or China.[53][54] Historically, the growth rate for electricity demand has outstripped that for other forms of energy.[55]:16
Environmental concerns with electricity generation have led to an increased focus on generation from renewable sources, in particular from wind and hydropower. While debate can be expected to continue over the environmental impact of different means of electricity production, its final form is relatively clean[55]:89
Early 20th-century alternator made in Budapest, Hungary, in the power generating hall of a hydroelectric station (photograph by Prokudin-Gorsky, 1905–1915).
Electrical power is usually generated by electro-mechanical generators driven by steam produced from fossil fuel combustion, or the heat released from nuclear reactions; or from other sources such as kinetic energy extracted from wind or flowing water. The modern steam turbine invented by Sir Charles Parsons in 1884 today generates about 80 percent of the electric power in the world using a variety of heat sources. Such generators bear no resemblance to Faraday's homopolar disc generator of 1831, but they still rely on his electromagnetic principle that a conductor linking a changing magnetic field induces a potential difference across its ends.[49] The invention in the late nineteenth century of the transformer meant that electrical power could be transmitted more efficiently at a higher voltage but lower current. Efficient electrical transmission meant in turn that electricity could be generated at centralised power stations, where it benefited from economies of scale, and then be despatched relatively long distances to where it was needed.[50][51]
Wind power is of increasing importance in many countries
Demand for electricity grows with great rapidity as a nation modernises and its economy develops. The United States showed a 12% increase in demand during each year of the first three decades of the twentieth century,[52] a rate of growth that is now being experienced by emerging economies such as those of India or China.[53][54] Historically, the growth rate for electricity demand has outstripped that for other forms of energy.[55]:16
Environmental concerns with electricity generation have led to an increased focus on generation from renewable sources, in particular from wind and hydropower. While debate can be expected to continue over the environmental impact of different means of electricity production, its final form is relatively clean[55]:89
Electronics
Main article: electronics
Surface mount electronic components
Today, most electronic devices use semiconductor components to perform electron control. The study of semiconductor devices and related technology is considered a branch of solid state physics, whereas the design and construction of electronic circuits to solve practical problems come under electronics engineering.
Electric power
Main article: electric power
Electric power is the rate at which electric energy is transferred by an electric circuit. The SI unit of power is the watt, one joule per second.Electric power, like mechanical power, is the rate of doing work, measured in watts, and represented by the letter P. The term wattage is used colloquially to mean "electric power in watts." The electric power in watts produced by an electric current I consisting of a charge of Q coulombs every t seconds passing through an electric potential (voltage) difference of V is
- Q is electric charge in coulombs
- t is time in seconds
- I is electric current in amperes
- V is electric potential or voltage in volts
Electric circuits
Main article: Electric circuit
A basic electric circuit. The voltage source V on the left drives a current I around the circuit, delivering electrical energy into the resistor R. From the resistor, the current returns to the source, completing the circuit.
The components in an electric circuit can take many forms, which can include elements such as resistors, capacitors, switches, transformers and electronics. Electronic circuits contain active components, usually semiconductors, and typically exhibit non-linear behaviour, requiring complex analysis. The simplest electric components are those that are termed passive and linear: while they may temporarily store energy, they contain no sources of it, and exhibit linear responses to stimuli.[47]:15-16
The resistor is perhaps the simplest of passive circuit elements: as its name suggests, it resists the current through it, dissipating its energy as heat. The resistance is a consequence of the motion of charge through a conductor: in metals, for example, resistance is primarily due to collisions between electrons and ions. Ohm's law is a basic law of circuit theory, stating that the current passing through a resistance is directly proportional to the potential difference across it. The resistance of most materials is relatively constant over a range of temperatures and currents; materials under these conditions are known as 'ohmic'. The ohm, the unit of resistance, was named in honour of Georg Ohm, and is symbolised by the Greek letter Ω. 1 Ω is the resistance that will produce a potential difference of one volt in response to a current of one amp.[47]:30-35
The capacitor is a development of the Leyden jar and is a device that can store charge, and thereby storing electrical energy in the resulting field. It consists of two conducting plates separated by a thin insulating dielectric layer; in practice, thin metal foils are coiled together, increasing the surface area per unit volume and therefore the capacitance. The unit of capacitance is the farad, named after Michael Faraday, and given the symbol F: one farad is the capacitance that develops a potential difference of one volt when it stores a charge of one coulomb. A capacitor connected to a voltage supply initially causes a current as it accumulates charge; this current will however decay in time as the capacitor fills, eventually falling to zero. A capacitor will therefore not permit a steady state current, but instead blocks it.[47]:216-220
The inductor is a conductor, usually a coil of wire, that stores energy in a magnetic field in response to the current through it. When the current changes, the magnetic field does too, inducing a voltage between the ends of the conductor. The induced voltage is proportional to the time rate of change of the current. The constant of proportionality is termed the inductance. The unit of inductance is the henry, named after Joseph Henry, a contemporary of Faraday. One henry is the inductance that will induce a potential difference of one volt if the current through it changes at a rate of one ampere per second. The inductor's behaviour is in some regards converse to that of the capacitor: it will freely allow an unchanging current, but opposes a rapidly changing one.[47]:226-229
Electromagnets
Main article: Electromagnets
Magnetic field circles around a current
Ørsted did not fully understand his discovery, but he observed the effect was reciprocal: a current exerts a force on a magnet, and a magnetic field exerts a force on a current. The phenomenon was further investigated by Ampère, who discovered that two parallel current-carrying wires exerted a force upon each other: two wires conducting currents in the same direction are attracted to each other, while wires containing currents in opposite directions are forced apart.[45] The interaction is mediated by the magnetic field each current produces and forms the basis for the international definition of the ampere.[45]
The electric motor exploits an important effect of electromagnetism: a
current through a magnetic field experiences a force at right angles to
both the field and current
Experimentation by Faraday in 1831 revealed that a wire moving perpendicular to a magnetic field developed a potential difference between its ends. Further analysis of this process, known as electromagnetic induction, enabled him to state the principle, now known as Faraday's law of induction, that the potential difference induced in a closed circuit is proportional to the rate of change of magnetic flux through the loop. Exploitation of this discovery enabled him to invent the first electrical generator in 1831, in which he converted the mechanical energy of a rotating copper disc to electrical energy.[46] Faraday's disc was inefficient and of no use as a practical generator, but it showed the possibility of generating electric power using magnetism, a possibility that would be taken up by those that followed on from his work.
Electric potential
- Main article: Electric potential. See also: Voltage, Battery (electricity)
A pair of AA cells. The + sign indicates the polarity of the potential difference between the battery terminals.
For practical purposes, it is useful to define a common reference point to which potentials may be expressed and compared. While this could be at infinity, a much more useful reference is the Earth itself, which is assumed to be at the same potential everywhere. This reference point naturally takes the name earth or ground. Earth is assumed to be an infinite source of equal amounts of positive and negative charge, and is therefore electrically uncharged—and unchargeable.[42]
Electric potential is a scalar quantity, that is, it has only magnitude and not direction. It may be viewed as analogous to height: just as a released object will fall through a difference in heights caused by a gravitational field, so a charge will 'fall' across the voltage caused by an electric field.[43] As relief maps show contour lines marking points of equal height, a set of lines marking points of equal potential (known as equipotentials) may be drawn around an electrostatically charged object. The equipotentials cross all lines of force at right angles. They must also lie parallel to a conductor's surface, otherwise this would produce a force that will move the charge carriers to even the potential of the surface.
The electric field was formally defined as the force exerted per unit charge, but the concept of potential allows for a more useful and equivalent definition: the electric field is the local gradient of the electric potential. Usually expressed in volts per metre, the vector direction of the field is the line of greatest slope of potential, and where the equipotentials lie closest together.[24]:60
lectric field
- Main article: Electric field. See also: Electrostatics.
Field lines emanating from a positive charge above a plane conductor
The study of electric fields created by stationary charges is called electrostatics. The field may be visualised by a set of imaginary lines whose direction at any point is the same as that of the field. This concept was introduced by Faraday,[38] whose term 'lines of force' still sometimes sees use. The field lines are the paths that a point positive charge would seek to make as it was forced to move within the field; they are however an imaginary concept with no physical existence, and the field permeates all the intervening space between the lines.[38] Field lines emanating from stationary charges have several key properties: first, that they originate at positive charges and terminate at negative charges; second, that they must enter any good conductor at right angles, and third, that they may never cross nor close in on themselves.[17]:479
A hollow conducting body carries all its charge on its outer surface. The field is therefore zero at all places inside the body.[24]:88 This is the operating principal of the Faraday cage, a conducting metal shell which isolates its interior from outside electrical effects.
The principles of electrostatics are important when designing items of high-voltage equipment. There is a finite limit to the electric field strength that may be withstood by any medium. Beyond this point, electrical breakdown occurs and an electric arc causes flashover between the charged parts. Air, for example, tends to arc across small gaps at electric field strengths which exceed 30 kV per centimetre. Over larger gaps, its breakdown strength is weaker, perhaps 1 kV per centimetre.[39] The most visible natural occurrence of this is lightning, caused when charge becomes separated in the clouds by rising columns of air, and raises the electric field in the air to greater than it can withstand. The voltage of a large lightning cloud may be as high as 100 MV and have discharge energies as great as 250 kWh.[40]
The field strength is greatly affected by nearby conducting objects, and it is particularly intense when it is forced to curve around sharply pointed objects. This principle is exploited in the lightning conductor, the sharp spike of which acts to encourage the lightning stroke to develop there, rather than to the building it serves to protect[41]:155
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