Voltage, Current, Resistance and Ohm's Law

Voltage, Current, Resistance and Ohm's Law
 

When electrons are separated from atoms – either through friction (eg, static electricity), chemical reaction (eg, a battery), electromagnetism or other phenomenon – an electrical field is formed, consisting of two oppositely charged terminals, and an associated “tension” or “pressure” between them.

The measure of this “tension” or “pressure” is known as voltage.

Atomic Structure

Atomic Structure.....
The atom is a basic unit of matter, consisting of a central nucleus (containing positively charged protons and electrically neutral neutrons), and surrounded by negatively charged electrons which move in 1 or more orbital “shells” around the nucleus.
For example, consider a carbon atom:

The number of protons in a nucleus is the atomic number, and defines the type of element the atom forms. Thus, carbon has an atomic number of 6.The number of neutrons in a nucleus determines the isotope of an element. For example, carbon-12 has 6 protons and 6 neutrons, while carbon-14 has 6 protons and 8 neutrons.
Most matter is said to be electrically “neutral”, since the #electrons = #protons. (Ions are atoms which are not neutral – ie, they have either gained or lost electrons).
An atom may have multiple electron “orbital shells”. In the case of carbon, the first shell contains 2 electrons, and the second shell contains 4 electrons.

A group of atoms may remain “bound” to each other, forming a molecule.

Binary Addition

The process for adding binary numbers is the same in any number system, except that you must be aware of when (and what) to “carry”.
In the decimal system, a carry occurs when the sum of 2 digits is 10 or more.  For example,

The Binary Number System.......

The Binary Number System..

The binary number system is a special code that the computer uses for representing numeric data. Numeric data is any value that can be used for mathematical operations such as addition and subtraction. This code is completely different than the ASCII system, except that only 1s and 0s are used.
For example, consider the code 01001010. In the ASCII system, this represents the letter “J”. However, in the binary number system, this represents the number 74.

ASCII and Unicode.............

ASCII - American Standard Code for Information Interchange
About the same time that IBM was developing EBCDIC, a group of engineers from the American Standards Association were developing another code for representing character data.  The result was ASCII - the American Standard Code for Information Interchange. 
ASCII used 7 bits to represent characters, giving 128 possible symbols.
Here is the original ASCII table from 1963.  Like EBCDIC, the grey areas represent non-printable control keys (Esc, Del, Backspace, etc.), as well as special characters used in data transmission.

To find the ASCII code for a particular character,

1. Locate the character in the table (for example, "J")
2. Write down the three "Low Order" bits on the left side of the table directly across from the character (for "J", they are 100).
3. Write down the four "High Order" bits at the top of the table, directly above the character (for "J", they are 1010).

BCD and EBCDIC

BCD and EBCDIC
BCD - Binary Coded Decimal
Early mainframe computers in the 1950s were programmed using numeric codes, not text.  As a result, the first coding system used in these computers only needed to represent the ten digits in our number system.  The BCD (Binary Coded Decimal) system used 4 bits to represent numbers as follows:

Therefore, to represent the number 253, the computer would store 0010 0101 0011.

Digital vs. Binary Data

Digital vs. Binary Data....
Humans use numbers that contain only ten different digits – 0 thru 9. The Latin prefix for ten is “dec”, hence, our number system is known as decimal.
Numeric values inside any electronic device are stored using only 2 distinct values – 1 and 0. The Latin prefix for two is “bi”, hence, the number system used inside electronic devices is known as binary).
For example,