ALTERNATING V/s DIRECT CURRENT
A short introduction to the direct and alternating current
Background
Background
Electrons
negatively charged sub-atomic particles whose movement in a medium results in flow of current.
Current
Flow of electrons. Physically, it is a measure of rate of electron flow through a particular point in an electric circuit. It is measured in units of Coulombs/s or Amperes.
Voltage or electromotive force
When current is flowing in a circuit, it implies, there is a movement of electrons. This movement is due to existence of electrical force, called electromotive force or voltage. It is measured in the units of Joules/Coulomb or Volts.
Literally electromotive force is a force that motivates electrons (to move).
The three common parameters in terms of which electricity is explained are current, voltage and power (current x voltage).
Electric currents are of two types:
(i) Alternating current
(ii) Direct current
negatively charged sub-atomic particles whose movement in a medium results in flow of current.
Current
Flow of electrons. Physically, it is a measure of rate of electron flow through a particular point in an electric circuit. It is measured in units of Coulombs/s or Amperes.
Voltage or electromotive force
When current is flowing in a circuit, it implies, there is a movement of electrons. This movement is due to existence of electrical force, called electromotive force or voltage. It is measured in the units of Joules/Coulomb or Volts.
Literally electromotive force is a force that motivates electrons (to move).
The three common parameters in terms of which electricity is explained are current, voltage and power (current x voltage).
Electric currents are of two types:
(i) Alternating current
(ii) Direct current
Direct Current
Direct Current results from flow of electrons in a single direction and with a constant magnitude (not entirely true). Such a current is produced by a battery, solar cell, etc. Examples of devices involving direct current are those which operate on batteries, for example, flashlight, portable radio, etc. The direct current can be represented graphically as shown below
A battery having negative (cathode) and positive (anode) terminals produces a direct current. The composition of the terminals varies with the type of battery being used. For instance, Lead Acid battery, the most commonly used rechargeable battery, has Lead and Lead dioxide as the two electrodes. Sulphuric acid mixed with water is the electrolyte which induces chemical reactions at both ends. This results in excess of electrons at the Lead terminal (cathode) and depletion of electrons at the Lead dioxide terminal (anode). Thus, a potential difference develops between the two terminals. Upon connection of an external load, current starts flowing from the terminal having excess electrons to the one having a deficit and performs required work on the way like lighting a bulb. Solar Cells and Fuel Cells also perpetuate direct current.
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| Figure 1: Direct current of magnitude IV. |
A battery having negative (cathode) and positive (anode) terminals produces a direct current. The composition of the terminals varies with the type of battery being used. For instance, Lead Acid battery, the most commonly used rechargeable battery, has Lead and Lead dioxide as the two electrodes. Sulphuric acid mixed with water is the electrolyte which induces chemical reactions at both ends. This results in excess of electrons at the Lead terminal (cathode) and depletion of electrons at the Lead dioxide terminal (anode). Thus, a potential difference develops between the two terminals. Upon connection of an external load, current starts flowing from the terminal having excess electrons to the one having a deficit and performs required work on the way like lighting a bulb. Solar Cells and Fuel Cells also perpetuate direct current.
Alternating Current
In alternating current electrons flow in one direction for a period of time; change direction; and then flow in opposite direction for the same period of time. Thus, there is continuous change in magnitude and periodical change in direction of the current.
In alternating current electrons periodically change direction within the wire, though, each of the electrons does not travel far. Rate of change of direction by the electrons is called frequency of alternating current and is measured in Hertz (Hz).
The alternating current can be represented graphically by a sinusoidal curve as shown below
The average value of alternating current in one complete cycle is zero. Therefore, root mean square value of alternating current (Irms) is used as its measure. By definition, Irms is the magnitude of a direct current which will generate amount of heat in a given time in a given resistance as the given alternating current .
Mathematically,
Irms=Imax/√2
The electricity that we get at our homes is an example of alternate current.
Alternating Current is produced by rotating a magnetic field around wire coils. This is based on the principle of electromagnetic induction, whereby, change in the magnetic flux through the area enclosed by a wire produces current in it. A magnet has two poles North and South. Once the polarity of the magnet reverses, the current changes direction. Faster the rotation of the magnet, quicker is the reversal of the polarity of the current. The frequency is generally 50-60 Hertz per second. Electrons travel back and forth between the two terminals producing a sinusoidal wave pattern.
Comparison between Alternating and Direct current
Alternating current transmits power at high voltage and low current. Thus, due to low current, power dissipation (loss) is low in alternating current. As electrons do not move very far in alternating current, losses due to friction are minimal even at very large distances. Hence alternating current is used to supply power to our homes from the power stations.
In addition, it can be stepped up or down, as required, by use of transformers at the point of usage. The idea behind usage of alternating current over direct current is that it results in saving energy loss besides transforming into higher or lower voltage levels. High voltages at power stations can be reduced to lower voltage by means of a transformer and used safely.
Direct current transmits power at low voltage and high current. Thus, it suffers from dissipation losses and can not be employed for transmission over large distances.
However, in cases where electricity is being used to dissipate heat, direct current may serve the same purpose because polarity of current is irrelevant.
THE ABOVE DISCUSSION CAN BE EXTENDED TO THE RESPECTIVE CASES OF ALTERNATING AND DIRECT VOLTAGES.
In alternating current electrons flow in one direction for a period of time; change direction; and then flow in opposite direction for the same period of time. Thus, there is continuous change in magnitude and periodical change in direction of the current.
In alternating current electrons periodically change direction within the wire, though, each of the electrons does not travel far. Rate of change of direction by the electrons is called frequency of alternating current and is measured in Hertz (Hz).
The alternating current can be represented graphically by a sinusoidal curve as shown below
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| Figure 2: Alternating current with peak value of Imax |
The average value of alternating current in one complete cycle is zero. Therefore, root mean square value of alternating current (Irms) is used as its measure. By definition, Irms is the magnitude of a direct current which will generate amount of heat in a given time in a given resistance as the given alternating current .
Mathematically,
Irms=Imax/√2
The electricity that we get at our homes is an example of alternate current.
Alternating Current is produced by rotating a magnetic field around wire coils. This is based on the principle of electromagnetic induction, whereby, change in the magnetic flux through the area enclosed by a wire produces current in it. A magnet has two poles North and South. Once the polarity of the magnet reverses, the current changes direction. Faster the rotation of the magnet, quicker is the reversal of the polarity of the current. The frequency is generally 50-60 Hertz per second. Electrons travel back and forth between the two terminals producing a sinusoidal wave pattern.
Comparison between Alternating and Direct current
Alternating current transmits power at high voltage and low current. Thus, due to low current, power dissipation (loss) is low in alternating current. As electrons do not move very far in alternating current, losses due to friction are minimal even at very large distances. Hence alternating current is used to supply power to our homes from the power stations.
In addition, it can be stepped up or down, as required, by use of transformers at the point of usage. The idea behind usage of alternating current over direct current is that it results in saving energy loss besides transforming into higher or lower voltage levels. High voltages at power stations can be reduced to lower voltage by means of a transformer and used safely.
Direct current transmits power at low voltage and high current. Thus, it suffers from dissipation losses and can not be employed for transmission over large distances.
However, in cases where electricity is being used to dissipate heat, direct current may serve the same purpose because polarity of current is irrelevant.
THE ABOVE DISCUSSION CAN BE EXTENDED TO THE RESPECTIVE CASES OF ALTERNATING AND DIRECT VOLTAGES.
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