Electrical Engineering

http://www.cisco.com/warp/public/473/lan-switch-transparent.swf http://www.cisco.com/en/US/tech/tk389/tk689/technologies_tech_note09186a00800a7af3.shtml Go through this link to understand them better. This will answer all your questions and let me know if you have any other question

maintained is where the light is constantly on all the time, For example,, when you go to cinema, There will be a maintained emergency light on the top of the exit door. This light will on constantly no matter the normal AC power outage or not.

Non-maintained is where the light is normally off until power loss or emergency situation. For example, In the corridor , there always a non-permanent emergency luminary & a normal luminary.

When the AC supply work well. We turn on the normal luminary to light the corridor by switch, The emergency luminary keep off.

Once the AC supply outage, the normal luminary can't work. The non-permanent emergency luminary will turn on automatically.

Cold climate 5W/30 Moderate climate 10W/40 Hot climate 20W/50.

Law of resistance: What you resist persists. based on the same concept as law of attraction

If it has the correct voltages on the coil and wont pull in to make contact - you replace it. If it pulls in then c;ean the contacts wit a point file and wd40.

A Schmitt trigger is a comparitor circuit that is basically an on-off switch. It's either on or off (which we call high or low). Once a threshold at the input is exceeded, it turns on, or goes high. Below the threshold, it turns off, or goes low. Drive a Schmitt trigger with whatever you want. It responds in only two ways; high or low. It has no other output states.

it measures the ionization of the air.

An SCR is a Silicon-Controlled-Rectifier. SCR's are used to turn on the AC supply voltage to a motor part-way into the AC cycle, thus allowing only part of the cycle through. Although the peak voltage reaching the motor may be just as high, the average or RMS value is less, since the voltage is not on as long. This type of control is called phase-angle control, as opposed to frequency control, which VFD's (variable frequency drives) do. Note the word 'rectifier' in the name. An SCR, just like any other diode or rectifier, only conducts in one direction, so for AC motor control, two SCR's must be used, one reversed from the other. One SCR fires during the positive half of the cycle, the other fires during the negative half of the cycle. Once the SCR is turned on, it latches, or stays on for the rest of the cycle. When the AC cycle half completes, and the voltage crosses zero, the SCR turns off. Thus the gate signal is usually a very short pulse, right at the moment the SCR needs to fire. Note that the SCR is not like a transistor. It cannot be turned part way on, it is either on or off. The latching action is also different. Transistors do not latch on by themselves. SCRs can also be used as an on-off controller. In this case, the SCR is either completely off (when the motor is to be stopped), or it is controlled on for the entire cycle (when the motor is to run). This type of control is used to replace the old mechanical relays or contactors. In fact, these controllers are called 'Solid State Relays'. Again, two SCR's are used. A similar device is called the Triac. It works basically the same as an SCR, except it conducts in both directions, so only one is needed instaead of two.

A electric Geyser has a Element screwed in the side of the inner water container,

with the heated side submerged in water, parallel to the element (sometimes center)

is a thermostat unit to control the temperature by switching the element off once the desired temperature has been reached. The element itself is made with nichrome wire,

which is a resistive wire, When a Electric current is passed through the nichrome wire

the resistance of the wire restricts the current causing a pressure of electrons and protons (as water builds pressure in a hose pipe when the end is restricted) and intern

creates heat as a byproduct.

well microorganisms found in food use the water in the Air to be able to work and multiply therefore spoiling your food. to be able to avoid this one as to check what is the spoilage exactly and know from which microorganism it is coming then researching the water activity lvel that this microorganism works at and just controlling the moisture to be less than that number

It depends on whether the transistor is in the active region or not. Usually, the transistor would be in the active region when we are asking this question. if we look at the data sheet for the popular 2N3905 transistor, available at http://www.fairchildsemi.com/ds/2N/2N3905.pdf,

we see that if V collector-emitter is 10 V, the collector current is 1 mA, and the small signal frequency is 1 kHz, the typical small signal signal input impedance (which is nearly the same as small signal base-emitter resistance) is about 5,000 ohms. Under the same conditions, the typical output admittance, (which is nearly the same as the small signal collector-emitter resistance) is about 30 microsiemens. Calculate 1/0.000030 to find that this is the same as about 33,000 ohms, so in this case the collector-emitter small signal resistance is greater than the base-emitter small signal resistance. You might be able to find an operating point where the reverse is true.

You should be able to search the NEC on the internet. However, local code may play a role in whether or not you can use aluminum in an underground application. The other consideration would be whether or not it's listed as a `direct burial wire`, which is to say, is the insulation manufactured to be buried underground.

I'm not a big fan of aluminum, and if you're trying to save some money now, you'll most likely end up having to replace it within 5- 10 years. There's also been a lot of house fires attributed to aluminum wiring as it tends to overheat easier than copper.

So search the code on the internet, search your local codes and then go with copper direct burial cable anyway. You'll be happier in the long run. But yes, local amendments notwithstanding, the standard NEC does allow aluminum conductors with the proper insulation rating to be used underground. If it is installed in an underground raceway, it must be listed for wet locations, or for direct burial if buried.

a bunch of tities a bunch of tities

resistivity and resistance are two diff. things...........resistance depends on length and thickness resisitivity too depends on the area and length resistivity=resistance*area/length

Unilateral circuits is consists of unilateral elements which allows the current flow in only one direction. It applies the electricity from one side to the other side just like an open circuit.

Depends on which one you have. Most are held in place by a small bolt and nut.

Two SCR's are connected in an inverse-parallel arrangement to one leg of a single phase circuit. This arrangement allows one SCR to control one half of the sine wave, and the other SCR controls the other. A special circuit is used, sometimes called a "trigger circuit". This circuit sends a pulsed signal to each gate of the two SCR's. The SCR's are so fast to open close the circuit, that they can be "fired" open, then "shut" off in increments far smaller than 1/60th of a second, the typical AC line frquency. So, if you were to tell the trigger circuit to fire each SCR for only 1/240th of a second, (1/2 of 1/2 of a complete cycle) 60 times a second, then each SCR would only be "on" or letting electric current through for 1/2 of each +/- cycle of the sine wave. Therefore output power would be 50% of maximum, but complete in the sense that the 60Hz cycle would remain intact. To put it another way you would still have an alternating current 60 times per second, but the upper and lower portion of the sine wave would be cut off early, and at the same points respectively. This is called Phase-Angle Control, and is the most common form of solid state power control. Resistive loads are the easiest to control with solid state techniques, though power factor is increased with the use of solid state switching. There are ways around that. The advantages of this type of power control is infinitley variable power output, with no mechanical contactors to wear out. SCR's can switch 100's of amps, hundreds of times per second, and as long as you keep them cool, theoretically they will never wear out. If you would like to know more, there is a site: http://www.payneb5.com , for Payne Engineering. They have a couple of animations and schematics depicting what i just explained, but with pictures.

Power lines don't hum, but the transformers that run them do. The humming is a result of the interchange in the coils that converts the voltage to a different level.

Let me first correct the question "current" here should be "tension" current is the speed of the electrons moving through the conductor and tension is the EMF that make the electrons move you cannot input current. the current is the demand of the circuit, depending on the resistance and the EMF(Electro Motoric Force) in other words, the Volts that is applied or input to the circuit.
Answer:
Any transformer can be used as a up step(inverting) or down step(converting) transformer, for instance 220V - 6V will be a converting and the 220V side will be your primary or high tension input and if you turn it around the 6V side will be your primary or low tension input.

The factors of electricity are the voltage between two points and the amount of current experienced.

Yes. Transformers operate on the theory of inducing current in one coil by starting and stopping the current in another coil on the same iron core. The voltage changes as a function of the turns ratio of the primary (driven) side to the secondary (output) side. Alternating current changes rapidly each second (e.g., 50, 60 400 Hz). To use a transformer in DC-to-DC converters, you first need to create a wave, run it through the transformer to get the new voltage, then rectify and filter it to restore the output to a DC voltage. Is this a trick question? AC in and AC out. Straight DC won't work without help. The DC is "switched" or "chopped" or "turned on and off" quickly in the primary, and this action will allow the pulsating DC in the primary to drive the secondary of the transformer. Problem solved.

To cable means to make a cable stitch pattern on a knitted garment. This stitching pattern makes a twisted cord effect on a sweater. It is particularly popular on fisherman's sweaters. It is a raised decorative effect done generally in the same color as the body of the sweater. The cable stitch is a pattern, but it is a repeating pattern that does not change within the garment. Since the pattern will generally give you the stitch directions for one cable, it refers to this particular bit of instruction as "to cable" or "cable stitch". In general, to cable means to use this bit of knitting as a repeating pattern within a garment direction. What will happen within the pattern is this. The pattern will give direction for one cable and then say "cable" and continue on with the directions for other items within the pattern. Things such as bobbles and raised diamonds are a larger pattern item than a cable, so the pattern expects you to make your cable twists as you do in the pattern without having to write the directions every time. You should be an experienced knitter if you attempt a cabled pattern. If you are having problems with the pattern, try this. Write down the cable pattern separately as rows, count the rows, and rewrite the pattern so that you can see where this pattern counts in the other pattern. Once you do this, the cabling process will go much faster.

Count the number of stacked "rings" on the insulator and multiply by 10kV; this will give you a rough estimate. THAT IS B.S. TRANSMISSION IS 500KV SO YOUR FRIEND WANTS 50 OF THOSE B.S. THAT IS NO CORRELATION TO THAT. BUT DISTANCE IS A VERY GOOD FACTOR TRUST ME ON THAT.