Chapter 23 Electronics and Computers

23-1 Semiconductor Devices Semiconductors are elements that conduct electricity under certain conditions. These are metalloids; elements located on the periodic table between metals and nonmetals. They are less conductive than metals but more conductive than nonmetal insulators.

23-1 Semiconductor Devices Semiconductors are used in calculators, cell phones, remote control cars, computers and many other electronic devices. Common semiconductors include silicon and germanium. Ever heard of Silicon Valley? Silicon Valley is the original home to the semiconductor chip making industry that uses silicon as a basic raw material, prompting a newspaper writer one day to call it Silicon Valley.

23-1 Semiconductor Devices The conductivity of semiconductor crystals can be increased by adding “impurities” in a process called doping. Doped silicon is a commonly used semiconductor. Silicon is often doped with arsenic or gallium. Arsenic doped silicon has more electrons than pure silicon so it is called an n-type (negative type) semiconductor; whereas gallium atoms have fewer than 4 electrons so it is called a p-type (positive type) semiconductor. By controlling the type and amount of doping, semiconductors with a variety of conducting properties can be created.

23-1 Semiconductor Devices Cellphones run off battery power which is direct current (DC) are charged by plugging it into the wall which provides alternating current (AC). Chargers contains transformers which reduces the voltage and rectifiers which change AC to DC. Household appliances are built to operate on DC. For simple devices such as smoke detectors and clocks batteries are used but for TVs and computers transformers and rectifiers have to be wired into the circuits. A diode is a type of rectifier made by doping the ends of a crystal to create one end with a p-type semiconductor and the other end with an n-type semiconductor. Electrons flow easily from the n-type end to the p-type end. This is called a pn-diode.

23-1 Semiconductor Devices A transistor is a semiconductor that amplifies an electrical signal. Amplifiers use transistors to amplify sound. Microphones, guitars, keyboards and electronic drums use the transistors to send out electronic sound. The signal travels many miles from a broadcast station to your stereo or TV receivers and is too weak to produce the picture or sound we need. The small input signal supplied to the transistor results in a large output current that can vibrate the speaker.

23-1 Semiconductor Devices Before transistors were invented, devices called vacuum tubes were used to amplify electric signals. Today's TVs and radios are much smaller. Today many tiny transistors work within a computer to calculate and transmit binary codes ( 1’s, 0’s ) to other transistors. The transistors work as a group called an integrated circuit. An integrated circuit can contain thousands of resistors, diodes and transistors on a thin slice of silicon. Integrated circuits allow computers to rapidly process information which increases their speed.

23-2 Radio and Television We've studied electromagnetic waves and electricity. Let's put the concepts together to explain radio and television. 1. At the radio station, a microphone changes compressional sound waves into electrical signals. 2. These signals are then amplified and passed through a modulator. (two types amplitude modulated or AM waves or frequency modulated or FM waves) 3. The electric currents are amplified and sent to an antenna, where they are transformed into radio waves. 4. Your radio has an antenna that “collects” the radio waves and transforms them into electrical current. 5. The radio's loudspeaker vibrates to cause sound waves for you to hear.

23-2 Television Televisions work the same as radios but they also use the electrical signals to create a visual image. Audio or sound signals are sent as FM signals and the video images are sent by AM carrier waves. A TV station simultaneously transmits the audio and video signals from its antenna. The most popular flat screen TVs are either LCD (liquid crystal display) or plasma. Flatscreen televisions are making the old CRT (cathode ray tube) TVs obsolete. Cathode-ray tubes use electrons and fluorescent materials to produce images on a screen.

23-3 Computers

The first computers operated on complex circuits composed of thousands of vacuum tubes. They used a lot of energy and were large enough to fill entire rooms. In the 1970's, the microprocessor was developed. It is an integrated circuit on the main circuit board. It functions as the brain of the computer telling other parts how to respond. Microprocessors reduced the size and cost of computers while increasing speed and reliability. In the 1980's, computers became available as household items and became as common as TVs and telephones in the home. Today, computers are fully programmable and portable and found in forms like smart phones and iPads.

23-3 Computer Memory Information is collected and stored in the memory of computers using a binary code. Each 1 (on) or 0 (off) represents one binary digit and is called a bit. Numbers, letters and symbols are grouped in arrangements of 8 bits called bytes. Often computer memory is expressed in terms of larger units such as megabytes - “million” or gigabytes - “billion”. Computers have several kinds of memory. Temporary memory is called “random access memory” or RAM and permanently stored memory is called “read only memory” or ROM. To be able to store needed information external storage devices such as thumb drives, portable hard drives, CDs and DVDs can be used.

23-4 Computer Crimes Computer crime is any crime committed with the help of a computer. Cyber crime in all its forms affects millions of people every year. Identity theft, hacking, fraud and illegal music downloads are just a few of the ways people are hurt by the internet. Cyber crimes are a major problem in the US and in Mississippi. Laws are continually being passed to protect individuals from computer crimes. As of 2011, Mississippi's cyber-bullying law reads as follows: Posting malicious messages on the internet (Facebook, MySpace, blogs, message boards, chat sites, etc.) is a FELONY in Mississippi, punishable by imprisonment for not more than five (5) years or a fine of not more than Ten Thousand Dollars ($10,000.00), or both. Miss. Code Ann. § 97-45-17.