Wikijunior:How Things Work/Mobile Phone
Who invented it?
The invention of the mobile phone, or cellphone as it is often called, is credited to Dr. Martin Cooper at Motorola. He made the first successful call over the system on April 3 of 1973.
How does it get power?
All portable cellphones use an electrical battery.
The batteries are usually rechargeable, so they can be used over and over again with recharging. To recharge the battery, the cellphone is plugged into a charger that connects to either a car battery or an electrical wall socket. Charging stores electrical energy onto the battery, which is then slowly used up by the cell phone after it has been unplugged.
Most cellphones typically use a 3.6 volt battery. The battery will usually last 2-3 days before it needs to be recharged depending on how much the phone is used.
How does it work?
The cellphone is a combination of a telephone and a radio. Like a telephone, you can listen and talk to someone on the other end, and like a radio, you can do it wirelessly over the air. The signals that come into and go out of a cellphone are like the ones TV and radio are received on, just formatted differently.
Signals are sent back and forth between the cellphone and a base station. The base station is a device that is usually a mile or two away from where the cellphone is being used and has an antenna that is high up on a tower. Since radio signals can bounce around and go through walls and windows, you don't have to be within sight of the base station in order to communicate with it. Once the signals arrive at the base station, they are converted into regular telephone signals and sent over the public telephone network to whomever you are calling, or sent back out from another base station if you are calling another cellphone.
The reason why it is called a cellphone is that it operates inside a "cell". A cell is a geographic region in which a base station is located. If you are located in that cell, your cellphone communicates to the base station inside that cell. If you move into a different cell, you are transferred seamlessly to a different base station inside the other cell. By keeping the cells small and having many base stations located every couple of miles, more users can talk at the same time from different places.
Also since there are many cells, one is located close to where you are using the phone, so the phone does not have to transmit with too much power. Less power means the phone can be made smaller and use less battery. Think of it as if you were at a party in a large room with a lot of people talking. If you were talking to a person just 3 feet way, you don't have to shout for them to hear you. Meanwhile, someone at the other end of the room could be talking to someone else near them and not interfere with what you are saying.
How dangerous is it?
When properly used a cellphone is not dangerous at all. A cellphone uses microwave frequency to communicate over the air to a base station. To do so, it transmits about 1 Watt of power from its antenna. You can compare that with the amount of power a single Christmas light bulb consumes.
Since talking on a mobile phone is distracting, it can be dangerous to use one while driving. Several studies have shown that drivers have more accidents while using cellphones, even when using "hands-free" systems. Many countries and some U.S. states have passed laws to restrict use of mobile phones while driving.
Many gas stations have signs warning people not to use mobile phones while pumping gas. There is a small chance that a broken cellphone can cause a spark that can ignite gas vapors. Although this is very unlikely, it's best to be safe than sorry, and not use electronic equipment such as mobile phones where explosive gas may be present.
What does it do?
A mobile phone allows you to use telephone service from almost anywhere. Most telephones are what is called "land line" or "fixed line" meaning they are physically tied to the land by a wire that plugs into a jack that goes to the phone company. A portable or cordless phone allows you to talk wirelessly but the receiver is still connected to the same land line. The cordless phone can only work within 100 - 200 feet of your receiver that is connected to the land line.
A mobile phone allows you more range and allows you to communicate much further from virtually anywhere in the city, country, or world. You have the ability to make a telephone call or receive one wherever you happen to be with your mobile phone. But only if you have a signal.
How does it vary?
Mobile phones or cellphones come in many different configurations. Most are about the size of a candy bar, have a display and a keypad. Some configurations come with a flip that opens up to show the display and the keypad, thereby keeping it protected.
Cellphones are available both big and small, simple and complex. Some just make simple phone calls, others have tiny cameras, MP3 players, digital organizers built into them. Some of the newer models, can even allow you to use the internet over them, browse various services such as news, movie listings, or chat using instant messaging services.
New models are always being introduced. New fashions, new technology, more features, cheaper cost, better performance, keep the market place filled with plenty of choices.
How has it changed the world?
The mobile phone has radically changed the world since its introduction in 1973. With each year more and more people are owning one. Most families typically have two or three.
The ability to easily communicate to anyone, anywhere, is a powerful concept. This was true when the telegraph was first invented, and then taken to a new level with the advent of the telephone. The mobile phone is just the next extension of that technology.
Ease of communication, leads to more efficient communication, and thus to an efficient use of time and resources. More efficient communication leads to better collaboration, better ideas, better use of time, more peace of mind. It provides an important lifeline in times of emergency.
But aside from practical applications, it also provides benefits socially and is fun. It allows communications with friends and family regardless of location. Whether you're calling to say something important, or just to chat about nothing at all.
Many mobile phones now have cameras built into them, allowing you to take a photo anywhere at any time, some people buy mobile phones just for the camera and don't even use it to phone or text people!
Plenty of important events and controversies have happened because people could organise things quicker with mobile phones. In Britain, a series of strikes by cargo lorry drivers over rising fuel prices was supposedly organised by one man and a mobile phone. Mobile phones with cameras and video are increasingly being used to capture important events when television crews are not available.
What idea(s) and/or inventions had to be developed before it could be created?
Since the mobile phone is a combination of a telephone and a radio, these two devices are the building blocks upon which the mobile phone was developed. In addition, tiny computers (microprocessors) are needed to control the radio and its connection to the nearest base station.
The telephone was invented by Alexander Graham Bell in 1876.
The radio was invented by Guglielmo Marconi in 1896.
The microprocessor was invented by Gary Boone in 1971.
Marconi's patents for radio were revoked later, and Nikola Tesla's were re-instated for his invention of radio at a much earlier date.