Waves & the Functioning of Cellphones

1. Waves & the Functioning of Cellphones by: Ethan Brzana, David Gomez, and Hong Dang Trinh

2. Overview • Cellphones are pivotal in modern life. • Approximately 91% of adults owned cellphones in 2013 according to the Pew Research Institute. • Before cellphones, people who needed to communicate used two way radios. • For example, commercial truck drivers used two way radios to communicate with other drivers on the road. • However, the issue with these radios was the fact that only one person could speak at a time because both radios utilized the same frequency. • Radios also have a limited range but cellular phones have a much longer range.

3. The Physics Behind Analog Cell-Phones • Cellphones transmit data through the use of radio waves. • Essentially a more complex radio. • Cell phone towers transmit the data between cellular devices. • Before one can understand how cellphones work one must first understand how waves work. • One must also understand the concept of frequency and how it applies to waves.

4. Introduction to Waves • "A wave can be described as a disturbance that travels through a medium from one location to another location [where the medium can be described as] a collection of interacting particles" (The Physics Classroom). • It is essential to know that waves are an energy transportation phenomenon. The way this works is that "as a disturbance moves through a medium from one particle to its adjacent particle, energy is being transported from one end of the medium to the other" (The Physics Classroom). • Waves transport energy without actually interacting with the end result. This will be a very important thing to keep in mind as we explain the way cell phones work.

5. Energy Transportation Phenomenon • The key point to remember is that waves transport energy without transporting matter: "Each individual particle of the medium is temporarily displaced and then returns to its original equilibrium position" (The Physics Classroom). • To illustrate this concept, think about a water wave. • As the disturbance (wave) passes through the medium, energy is transported, but the particles of the medium (water molecules) stay in the same place after vibrating. In other words, the particles of the medium "simply vibrate about a fixed position as the pattern of the disturbance moves from one location to another location" (The Physics Classroom). • This serves as proof that waves transport energy without transporting matter, and that is why waves are said to be an energy transportation phenomenon.

6. What Are Radio Waves? • Waves are invisible signals that move through the air and transmit various types of data such as pictures, words, conversations, and music • Composed of sinusoidal waves (sine waves) • Radio waves use different frequencies which allows many people to use things such as televisions, radios, and cellphones at once. • Frequencies will be explained more in depth in the next slide.

7. What is Frequency? (Hz) • Frequency is defined as the number of times something occurs per unit of time. • When referring to waves, frequency is the amount of times a wave vibrates through a medium per a set time. • The formula used to find the frequency of a wave is given by frequency equals one divided by the period of the wave or by velocity. • For example, if a wave oscillates through a medium thirty-two times in two seconds the wave has a frequency of sixteen hertz. • The unit used to measure frequency is called Hertz, abbreviated Hz. • Using two different frequencies allows two people to speak on a cell-phone at once.

8. Before Cell-Phones • There are two main methods in which cell phones and radios can communicate. • CB radios and walkie-talkies are half-duplex devices. • Half Duplex devices use only a single frequency to communicate which is why only one person’s voice can be heard at a time. • Cell-phones, however, are full-duplex devices which uses a frequency for listening and another for talking.

9. How Do Waves and Frequency Relate to Mobile Phones? • Waves and frequency make cellular communication possible. • Cellphones utilize radio waves to transmit data from one phone to another. • There are about 800 different frequencies that can be used with mobile phones. However, although this number seems large, it is not nearly enough to accommodate the volume of calls on a cellular network.

10. How Analog Cellphones Work • Due to the fact that two different frequencies are needed to complete a call only four hundred people can use cellphones at a given time. • This clearly presented an issue because of the sheer number of cellphone users. • However, cellphone carriers divide cities into cells which subsequently forms a grid that resembles a honeycomb. • These individual cells each contain around fifty-six channels which means fifty-six people can talk on their phones at the same time within the same cell. • It is worth mentioning that digital cell-phones which are used currently have many more channels than analog cell-phones which allow hundreds of people to use their phones within a single cell. • But, when an influx of people try to use their cell-phones at once and the cell exceeds capacity the transmission will not go through. • Football games at Beaver Stadium a prime example of cells being overloaded.

11. Cell Network Representation Each individual spans across about ten miles and a call can be transferred to different cells within the grid as a person moves around.

12. Connection Between the Way Cellphones Work and Waves • Cellphone communication results from electromagnetic waves transporting energy without particles from the source having to interact with particles at the end of the receiver. • What this means is that being able to speak with someone else in another location through the use of cellphones is a result of the following property: Waves transport energy without actually interacting with the end result . • In the case of cellphones, vibrating the electrons from the source creates electromagnetic waves that vibrate the electrons at the end of the receiver. Therefore, the electromagnetic waves transport energy without the electrons from the source having to interact with the electrons at the end of the receiver. • This is a key understanding of the relationship between the way cellphones work and waves.

13. Cell-Phone ID Codes • Cell-phones use codes to communicate with one another within the network. • Referred to as System Identification Codes (SIDS), they allow the phone that is placing the call to verify that the phone it is connecting to is within the range.

14. What New Insights Have We Learned • Millions of people use cell phones in some form everyday in different forms, whether that be phone calls, texting, or sending other types of data. • However, many people have very little idea how cell phones actually work. • Cellphones rely on many physics concepts like waves, frequency, and electricity to function. • By completing this project, we now have a greater understanding of how cellphones work. However, there are much more complex technologies on the market today like 4G LTE.

15. Insights Continuation • One of the most interesting insights this project provided us was the fact that electrons at the source do not have to interact with electrons at the end of the receiver. The reason for this is that electromagnetic waves created by the vibration of electrons transport energy. This is an example of a clear connection between our project and the concept that we learned in class that says that waves transport energy without actually interacting with the end result.

16. Works Cited Brain, Marshall, Jeff Tyson and Julia Layton. "How Cell Phones Work" 14 November 2000. Web. HowStuffWorks.com. http://electronics.howstuffworks.com/cell-phone.htm Brain, Marshall. "How Radio Works" 07 December 2000. Web. HowStuffWorks.com. http://electronics.howstuffworks.com/radio.htm Keith, Robert D. "How Cell Phones Work." 2004. Web. http://iml.jou.ufl.edu/projects/fall04/keith/Works.htm The Physics Classroom. "The Frequency and Period of a Wave." Web. April 2014. http://www.physicsclassroom.com/class/waves/u10l2b.cfm The Physics Classroom. "What is a Wave?" Web. April 2014. http://www.physicsclassroom.com/class/waves/Lesson-1/What-is-a-Wave.