Introduction to AC and DC Current

AC means “Alternating Current” and DC means “Direct Current.” AC and DC are also used when referring to voltages and electrical signals, which are not currents. DC is electricity flowing in a constant direction, and/or possessing a voltage with constant polarity.

DC is the kind of electricity that a battery with definite positive and negative terminals makes, or the kind of charge that is generated by rubbing certain types of materials against each other. Certain sources of electricity (most notably, rotary electro-mechanical generators) naturally produce voltages that alternate in polarity, reversing positive and negative over time. Either as a voltage switching polarity or as a current switching direction back and forth, this "kind" of electricity is known as Alternating Current (AC).

What is Alternating Current (AC)

Alternating Current (AC) flows one way, then the other way, continually reversing direction. An AC voltage is continually changing between positive (+) and negative (-). The rate of changing direction is called the frequency of the AC and it is measured in hertz (Hz), which is the number of forwards-backwards cycles per second. An AC supply is suitable for powering some devices such as lamps and heaters but almost all electronic circuits require a steady DC supply.

 
This shape portraying AC from a power supply is called a sine wave. Alternating current is the most common form used in the transmission of electricity from power plants to homes and businesses. It is convenient because the voltage can be changed easily with transformers. High voltage is good for long-distance transmission of electricity because it means less current has to flow to achieve the same amount of power, and power is lost in the resistance of wires in proportion to the square of the current. Alternating current is generated at the power station by rotating a coil of wire inside a big magnet. The energy needed to make the coil turn is provided by burning fuels such as coal, oil, natural gas, or by harnessing air, water, or nuclear power to do it. Faraday's law of induction relates the change in the voltage around the coil of wire to the rate of change of the amount of magnetic flux through the wire. If the wire turns around in circles, the voltage will be positive, then negative, then postitive again. Because the voltage swings back and forth between positive and negative values, at some times it crosses zero.

What is Direct Current (DC)

Direct Current (DC) always flows in the same direction, but it may increase and decrease. DC voltage is always positive (or always negative), but may increase and decrease. Electronic circuits normally require a steady DC supply which is constant at one value or a smooth DC supply which has a small variation called ripple.
Cells, batteries, and regulated power supplies provide steady DC which is ideal for electronic circuits.

Power supplies contain a transformer which converts the mains AC supply to a safe low voltage AC. The AC is then converted to DC by a bridge rectifier. However, the output is varying DC which is unsuitable for electronic circuits.

Direct current is very useful in powering small things such as flashlights and radios and toys. Batteries are the most common source of direct current -- the voltage of a battery is constant. Things that need lots of power in the form of direct current, like computers, have power supplies inside which transform alternating current from the wall plug to direct current. This way, they don’t run out of batteries.
 

Steady DC

from a battery or regulated power supply, this is ideal for electronic circuits.
 

Smooth DC

from a smoothed power supply, this is suitable for some electronics

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Reference links:

• http://www.science.howstuffworks.com › ... › Physical Science › Electricity
• http://www.allaboutcircuits.com › ... › BASIC AC THEORY
• http://www.hyperphysics.phy-astr.gsu.edu/hbase/electric/elevol.html

Gene – The Hereditory Material

Gene is a nucleic acid segment which contains the genetic information necessary to produce a protein. Genes have a long strand of DNA with a promoter. This promoter controls the gene activity and a coding sequence.







The gene coding determines what the gene produces. The informations present in the genes pass on to next generation. The organelle mitochondria self-replicate and they are not coded for by the organism's DNA.
 
Genes and its Bases
The genes are having 4 nucleotide bases  and hence named as polynucletides. Each nucleotide made up of a base group, a sugar and one ore phosphate groups.

1. Adenine(A)
2. Thymine (T)
3. Guanine (G)
4. Cytosine (C).
   
   
   
   
   •    The bases Adenine(A) and Guanine(G) are Purines
   •    Thymine (T) and Cytosine (C) are Pyrimidines.
   

Base Pairs
The sugar group is the backbone of DNA. The phosphate group links one nucleotide to another. The nitrogenous bases holds each other with the help of complimentary bases. Adenine is complimentary to Thymine while Guanine is complimentary to Cytosine. A forms 2 hydrogen bonds with T while G forms 3 hydrogen bonds with C.

So the  G≡C bond is more stable than an A=T bond.

Definition of Gene
The gene is a "A locatable region of genomic sequence, corresponding to a unit of inheritance, which is associated with regulatory regions, transcribed regions, and or other functional sequence regions"
Gene may refer to an allele:
•    A gene is the basic instruction, a sequence of nucleic acid
•    An allele is one variant of that gene.
The genetic changes can be observed in the single letter of the genetic code and this change is termed as ‘ a single nucleotide polymorphism’.

The expression of genes
The gene expressions encoded in DNA. It begins by the transcription process into RNA. RNA contains the nitrogenous base – uracil in place of thymine of DNA. RNA molecules are  single stranded and thus they are less stable than DNA.

Genetic Code
Genes that encode proteins are composed of codons. The codons are the series of three-nucleotide sequences. For example AUG,  AGG etc.This is the gene lanugauge and it is alomost same for all organisms.

 
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eAgeTutor.com is the premium online tutoring provider.  Using materials developed by highly qualified educators and leading content developers, a team of top-notch software experts, and a group of passionate educators, eAgeTutor works to ensure the success and satisfaction of all of its students.  
Contact us today to learn more about our guaranteed results and discuss how we can help make the dreams of the student in your life come true!