Electronics Engineering

It is much more efficient to transmit AC over long distances.

Because using transformers you can convert to very high voltages, and then power transmission then involves much lower currents, so that losses in the transmission line I2R are much reduced. You cannot easily and efficiently convert DC to high voltages.

A; BUFFER is used for isolation, translation of levels and amplification if needed

Often we want to easily change a resistor value, so we use a variable resistor.

For example, we may want to change the resistor that controls the power sent to a LED, so we can easily make it brighter or dimmer.

Often if we use a variable resistor, there is only a very narrow range that is useful.

Continuing our example, sometimes we use several LEDs, and we use the variable resistor to set them all to the same brightness.

In this case, the resistance range that sets the LED to be twice as bright as the the other LEDs, and the resistance range that sends so much power to the LED that it is permanently destroyed is even less useful.

So we add a fixed resistor in series with the variable resistor -- the fixed resistor sets the minimum net resistance, no matter how we turn the knob on the variable resistor.

In our example, the addition of the fixed resistor allows us to turn the variable resistor throughout its whole range, and the LED gets brighter and dimmer; without that resistor, a certain range of the knob on the variable resistor would allow so much power to go to the LED that it would be destroyed.

A: Transmission lines while there is ceramic insulators providing separation to the phases will have a corona if the insulators are dirty providing small current leakage ionizing the air around it therefore corona effect.

A: Mica is an insulator used extensively in capacitors and hi quality transformers. It has very good temperature coefficient

EIA-232 is designed to have only one transmitter and receiver connected by a bus connection (usually two wire). EIA-485 is designed to have up to 32 transmitters and receivers on a single bus. In 485, only one station can transmit at a time, but it can send to all 32 receivers. So a 485 transmitter must be able to be switched off so it is not affecting the bus. Also any transmitter must be able to provide enough drive to the bus for 32 receivers. There are limits on how much one receiver can load the bus.

EIA-485 is only the electrical specification. It does not address how the signals are encoded, how the stations share the bus, protocols, or the effect of propagation delays. There are several standard protocols based on EIA-485 as a lower layer.

The voltmeter would read 12 volts. An ammeter connected to to battery would only read 4 amps (12 volts divided by 3 ohms =4)

A cathode ray tube (CRT) was the main way images were presented to people before LCD, Plasma and LED screens were produced.

Everyone who watched television or used a computer before 1996 or so watched CRT screens.

'Tappings' are externally-accessible electrical connections to the turns of a transformer's (usually high-voltage) winding. This enables the number of turns to be changed, resulting in a change to the transformer's turns ratio and, therefore, to its voltage ratio.

Tap changing enables the electricity network company to adjust the turns ratio in response to any excessive voltage reduction resulting from a heavy load.

the envelope of AM immediately increased because the process of modulated had been doing at that same time. It mostly using the simple formula .

The impedance of a transmission line (Zo) should be matched from the source of the RF into the antenna. A bad match results in loss of output power and RF reflections up & down the transmission line. Standing Wave Ratio (SWR) meters are available to measure these reflections and enable them to be tuned out. Adjustment of antenna length for best SWR (1:1) is common. More mathmatical approaches are available on the web.

V = I * R

V = voltage

I = curernt

R = resistance

A: A LED is a diode and like all diode they have an [anode] meaning positive terminal and a [cathode] negative terminal. Therefore the proper potential must be applied for it to behave like an LED.

used as wave form generators like sinusoidal and non sinusoidal,

The maximum base thickness in a BJT is dependent on a number of variables and parameters (or call them "constraints").

You could create a base region with thickness ranging from a few layers of atoms up to the point where the "base" region responds to the models of bulk semiconductor by messing with the process parameters. But why?

If the base is too thick then with the transistor biased into the 'active' region (i.e., B-E junction forward biased & B-C junction reverse biased), the transistor 'alpha' (the ratio of carriers collected by BC to those generated in BE) will be hopelessly low and the transistor will not exhibit the high current gain that you expect from BJTs.

That's because a thick base provides too much opportunity for large numbers of forward current charge carriers to be recaptured by the crystal matrix or lost to the collector current in other ways.

the impurity add here is 1 atom of per million atoms of semiconductor.......

Bad frequency aliasing. See Nyquist criteria.

A shorted capacitor is one where the gap between the plates is damaged, and the plates are touching each other, creating a short circuit.

A logical analyzer is a device that is used to calculate and display digital signals. This is used to debug and evaluate the errors and find improvements that can be performed in digital systems.

For whole house audio, you need a "whole house amp". Another name for this is a "distribution amp". The companies that make these are Russound, Nuvo Technologies, Xantech, Elan, and others. These amps can typically serve 6 "zones" of speaker pairs (total 12 speakers) pumping audio signals from up to 6 "sources" (MP3, CD, AM/FM, Sirius, etc). Simply picking an amp is not enough since the amp merely powers, and distributes the source audio. Once you have source audio, you will also need the ability to control these sources from around your house, and from each "zone". Therefore a whole house audio system is usually comprised of a whole house amp, several audio sources, a pair of speakers per zone, and a remote keypad located in each zone. Keep in mind, for larger "zones" like a big room or an outdoor patio, you will need more than one pair of speakers. However since most whole house amps can only power one pair of speakers per zone, you will need to pursue a variety of options including a separate "power amp" dedicated to just that zone.

b class means the product did not pass the manufactures top quality check. It could be cosmetic or a slight defect. Usally does not affect product operation and you may not even notice any problem with the device. It will not be warrantied through the manufacture because it was sold at a lower price because of the rating. b class does not mean refurbushed. you are taking a "slight" risk of the product failing, but usally the seller will warranty the product for 1 yr. Most times if the product doesn't fail withing a few weeks, it is usally ok.