Waves & the Functioning of
Cellphones
by: Ethan Brzana, David Gomez, and Hong Dang Trinh
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.
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.
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.
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.
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.
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.
Before Cell-Phones
• There are two main methods in
which cell phones and radios can
communicate.
• CB radios and walkie-talkies are halfduplex 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 fullduplex devices which uses a
frequency for listening and another
for talking.
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.
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.
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.
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.
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.
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.
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.
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.