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This module discusses the graphing and plotting of logarithmic functions and some of their applications.

Suppose you want to graph the function y = log 2 ( x ) size 12{y="log" rSub { size 8{2} } \( x \) } {} . You might start by making a table that looks something like this:

x size 12{x} {} y = log 2 ( x ) size 12{y="log" rSub { size 8{2} } \( x \) } {}
1 0
2 1
3 um....I’m not sure
4 2
5 can I use a calculator?

This doesn’t seem to be the right strategy. Many of those numbers are just too hard to work with.

So, you start looking for numbers that are easy to work with. And you remember that it’s important to look at numbers that are less than 1, as well as greater. And eventually, you end up with something more like this.

x size 12{x} {} y = log 2 ( x ) size 12{y="log" rSub { size 8{2} } \( x \) } {}
1 8 size 12{ { {1} over {8} } } {} 3 size 12{ - 3} {}
1 4 size 12{ { {1} over {4} } } {} 2 size 12{ - 2} {}
1 2 size 12{ { {1} over {2} } } {} 1 size 12{ - 1} {}
1 0
2 1
4 2
8 3
As long as you keep putting powers of 2 in the x size 12{x} {} column, the y size 12{y} {} column is very easy to figure.

In fact, the easiest way to generate this table is to recognize that it is the table of y = 2 x size 12{y=2 rSup { size 8{x} } } {} values, only with the x size 12{x} {} and y size 12{y} {} coordinates switched! In other words, we have re-discovered what we already knew: that y = 2 x size 12{y=2 rSup { size 8{x} } } {} and y = log 2 ( x ) size 12{y="log" rSub { size 8{2} } \( x \) } {} are inverse functions.

When you graph it, you end up with something like this:

Coordinate plane graphing the log (base-2) of x
y = log 2 ( x ) size 12{y="log" rSub { size 8{2} } \( x \) } {}

As always, you can learn a great deal about the log function by reading the graph.

  • The domain is x > 0 size 12{x>0} {} . (You can’t take the log of 0 or a negative number—do you remember why?).
  • The range, on the other hand, is all numbers. Of course, all this inverses the function 2 x size 12{2 rSup { size 8{x} } } {} , which has a domain of all numbers and a range of y > 0 size 12{y>0} {} .
  • As x size 12{x} {} gets closer and closer to 0, the function dives down to smaller and smaller negative numbers. So the y size 12{y} {} -axis serves as an “asymptote” for the graph, meaning a line that the graph approaches closer and closer to without ever touching.
  • As x size 12{x} {} moves to the right, the graph grows—but more and more slowly. As x size 12{x} {} goes from 4 to 8, the graph goes up by 1. As x size 12{x} {} goes from 8 to 16, the graph goes up by another 1. It doesn’t make it up another 1 until x size 12{x} {} reaches 32...and so on.

This pattern of slower and slower growth is one of the most important characteristics of the log. It can be used to “slow down” functions that have too wide a range to be practical to work with.

Using the log to model a real world problem

Lewis Fry Richardson (1881–1953) was a British meteorologist and mathematician. He was also an active Quaker and committed pacifist, and was one of the first men to apply statistics to the study of human conflict. Richardson catalogued 315 wars between 1820 and 1950, and categorized them by how many deaths they caused. At one end of the scale is a deadly quarrel, which might result in 1 or 2 deaths. At the other extreme are World War I and World War II, which are responsible for roughly 10 million deaths each.

Number line showing the number of deaths on a large time line scale

As you can see from the chart above, working with these numbers is extremely difficult: on a scale from 0 to 10 Million, there is no visible difference between (say) 1 and 100,000. Richardson solved this problem by taking the common log of the number of deaths . So a conflict with 1,000 deaths is given a magnitude of log ( 1000 ) = 3 size 12{"log" \( "1000" \) =3} {} . On this scale, which is now the standard for conflict measurement, the magnitudes of all wars can be easily represented.

Number line showing the same number of human deaths on a logarithmic scale

Richardson’s scale makes it practical to chart, discuss, and compare wars and battles from the smallest to the biggest. For instance, he discovered that each time you move up by one on the scale—that is, each time the number of deaths multiplies by 10—the number of conflicts drops in a third. (So there are roughly three times as many “magnitude 5” wars as “magnitude 6,” and so on.)

The log is useful here because the logarithm function itself grows so slowly that it compresses the entire 1-to-10,000,000 range into a 0-to-7 scale. As you will see in the text, the same trick is used—for the same reason—in fields ranging from earthquakes to sound waves.

Questions & Answers

Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Logarithms. OpenStax CNX. Mar 22, 2011 Download for free at http://cnx.org/content/col11286/1.1
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