Electronics Engineering

Direct Current (DC) is an electric current flowing in one direction only.

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This question has become the point of much heated debate here on WikiAnswers, and I will attempt to pare down the answers to its simplest form while keeping all valid viewpoints intact. Any further debate should be put in the "Discussion" area.

The Case For Digital: With a few exceptions, a square wave in it's theoretical form will most likely be used in digital applications.

A square wave may be "analog" during the time it is in transition from one stable state to another, and "digital" when it is in one state or the opposite state (i.e., voltage level), according to the type of digital inputs stimulated, but a transition is not an analog state function in the context of computers or digital logic. A square wave has two states hi and low and the transition from hi to low can be switched up to gigahertz (GHz) frequencies. Test equipment manufacturers are able to generate square wave signals well above 100GHz. Function generators have the square wave signal where the transition can be controlled. Practically all digital circuits utilize these states as "1" and "0" (or true and false) that computers use to make decision at the machine language level. Furthermore all modern computer uses this signalling scheme. But digital signals (1's and 0's) are not necessarily "square" waves, strictly speaking. A clock circuit generates a square wave that is used as a timing reference for the address, data, and control circuits.

The Case For Analog: All theoretical waveforms look great on paper, but it is impossible to produce any perfect waveform. Therefore, all waveforms (including square waves) are inherently analog.

By Fourier Analysis, a square wave is actually an infinite series of the summation of sine waves, in this case the odd harmonics divided by N. As a result, a square wave can actually be considered an analog signal. Looking at this another way, no pulse driver, conductor, or transmission line is perfect, so the rise and fall time of a square wave are not instantaneous, meaning that the series is not really infinite so, again, the square wave is analog, although quite complicated, but still analog. We call it digital because we sense it with discriminators that decide the "value" of the wave based on some thresholds with appropriate hysteresis.

The Case For Sanity: A wave form is not inherently digital or analog. "Digital" and "analog" are arbitrary words used to describe an application of waveforms. In other words, all digital signals are square waves, but not all square waves are digital.

A square wave is usually used in digital applications, but is also used in audio applications for a "distorted" guitar or vocal effect. A sine wave can become a square wave if the input signal on an amplifier is too great for the power of the circuit to amplify, "clipping" the high and low portions of the sine wave.

A square wave can be considered an analog or a digital signal. A perfect square wave (not possible to generate based on Fourier Analysis) would not in general be considered an analog signal because it only has two values, defeating the point of analog (in many cases, but not all). One can make a square wave oscillator to use as an alarm - different frequencies were used to convey different information. A square wave was simple to create, thus my reason for using as opposed to a sine wave (this is an example of an analog use of square waves - the information is not stored in the two values of the wave, but in the "infinite frequency range made available by the extra circuitry to change frequencies."

This point is moot, really, because it is the nature of the data (being analog or digital) that truly is important, and defines whether the wave should be catagorized as "analog" or "digital".

Oh-So-Clever Analogy: A wrench is the perfect tool for fixing trucks, but if I use the wrench to fix a desk, that doesn't make the desk a truck. In short, the application defines the state, but does not limit the tool.

Resistance:

Electrical resistance describes how an electrical conductor (a wire) opposes the flow of an electrical current (flow of electrons). To overcome this opposition a voltage (a energy) must be dropped (used) across the conductor (wire). Resistance can be described by ohms law:

Ohms Law: R = V / I (Resistance = Voltage / Current) (resistance measured in ohms)

where:

Voltage [V]= the energy lost across an component (voltage measured in volts).

Current [I] = the charge (electrons) flowing through an component (current measured in Amps).

Electrical resistance can be thought of as sticking your hand out a car window. The faster [current] you drive the harder the wind presses [resistance] against you hand and therefore it takes more energy [voltage] to hold your hand steady.

When trying to overcome electrical resistance, the electrical energy lost is turned into heat. This is how the elements of a household stove, toaster, and fan heater work. Because of the vacuum in a light bulb, the electrical energy lost is instead turned into light. It can be seen that electrical resistance plays a large role in modern life.

Resistor:

The resistor is the most common electronic component and is used to limit and/or control the voltage and current in an electronic circuit. Resistors are carefully manufactured to provide a predetermined value of electrical resistance which may range from 0.1 ohms to 100,000,000 ohms, depending on the application. The physical size of a resistor also varies dependent on the amount of power passing through the resistor, given by:

P = V x I (Power = Voltage x Current) (power measured in watts)

There are also many types of resistors including:

· Variable Resistor - changes resistance when its shaft is rotated (volume knob on a stereo).

· Thermistor - changes resistance when the temperature changes (used in a thermostat).

· Light Dependant Resistor (LDR) - changes resistance when the lighting changes (used in children's night-lights).

Resistor Example:

An LED is a small red light (such as the one on the front of most TVs) and requires 2.0 volts and 0.02 amps to operate correctly. If we connected that LED up directly to a 12 volt battery, the voltage would be too high, and too much current would flow… the LED would blow up. We need to use a resistor to limit the voltage and current.

But which value of resistance should the have resistor? Uses ohms law:

R = V / I = (12.0 - 2.0) / 0.02 = 500 ohms

(Note: the voltage across the resistor is the battery voltage minus the voltage we want across the LED)

But which value of power should the resistor be capable of handling?

P = V x I = (12.0 - 2.0) * 0.02 = 0.2 Watts

It is called the positive + terminal or post, just like you list. Electrons flow for the negative - to the + terminal contrary to popular belief.

Another Answer

As electrons flow through the external circuit from anode (negative terminal) to the cathode (positive terminal) , then the answer is 'cathode'.

it can be used any where, where we need the clock pulse train of low frequancy.

like a function generator contains.
astable multivibrator is used to produce waveforms
as Astable means the circuit is not set to one state or the other but rather oscillates between those states. Therefore the application is signal generation

No. The total voltage drop around a series circuit, per Kirchhoff's voltage law, is zero. However, it is true that the total voltage drop of all of the components except the battery is equal and opposite to the voltage drop of the battery.

Interestingly, the formal definition of electromotive force is based on Kirchhoff's Voltage Law: 'A source's electromotive force is equal to the sum of all the voltage drops around a closed loop, including the source's internal voltage drop'.

Expressed as per the original answer, we could also say; 'The algebraic sum of a circuit's electromotive force and voltage drops, including the source's internal voltage drop, is zero'.

Hi,

1) Digital signals do not get corrupted by noise etc. You are sending a series of numbers that represent the signal of interest (i.e. audio, video etc.)

2) Digital signals typically use less bandwidth. This is just another way to say you can cram more information (audio, video) into the same space.

3) Digital can be encrypted so that only the intended receiver can decode it (like pay per view video, secure telephone etc.)

There are others, but this is three of the biggies.

Hi!

Following are the Advantages of Digital Transmission over analog transmission.

1. The signal is exact. For example, Digital formats like PCM (Pulse Code Modulation) can hold the exact digital format of sounds.

2. Digital signals can checked for errors. Generally, all digital transmission methods use 'head labels' to provide better checking facilities. Head label may contain how many packets may need to complete the transmission, what is the sequence number of each packet of data, acknowledgment labels etc.

3. A variety of services can afford over one line. For example, IpTV connection can used to watch cable TV channels while browsing the Internet through a PC using same line. This line can also used to make a phone call at the same time.

4. Digital data can be compressed and therefore possible to pass over higher bandwidths. Any digital data; data, image, video, voice can be compressed.

5. More secure. Digital data can be encrypt using an encryption method. Only the dedicated receiver can decode the message.

6. Supports data integrity. Simple to integrate voice, video and data. Digital transmission provides easier way to integrate different digital formats.

7. Digital transmission provides higher maximum transmission rates via medium such as optical fibers. Typically, digital transmissions use less bandwidth.

Hope this will help you!

(H.W Thushara Indika from Bandarawela - Sri Lanka)