# Can someone please explain log scales/graphs?

Watch
Announcements

Page 1 of 1

Go to first unread

Skip to page:

We need to plot the sizes of dna fragments using a log10 base pairs on the y axis. The problem is I have no idea what any of this means. Where do I even start? I tried looking up videos and found some very simplified versions. Then some girl on my course started talking about using "antilogs" and I am extremely confused. If someone could give me a simple introduction to log scales I'd really appreciate it!

0

reply

Report

#2

if you had y axis values between 0.0001 and 1000000 it wouldn't really make sense to plot them on a linear scale so sometimes a logarithmic scale is used. The only thing you need to do is do log(y) for each value and plot those instead. log should be base 10 by default on a calculator but there will be a button that lets you choose the base

Last edited by Meowstic; 2 days ago

1

reply

(Original post by

if you had y axis values between 0.0001 and 1000000 it wouldn't really make sense to plot them on a linear scale so sometimes a logarithmic scale is used. The only thing you need to do is do log(y) for each value and plot those instead. log should be base 10 by default on a calculator but there will be a button that lets you choose the base

**Meowstic**)if you had y axis values between 0.0001 and 1000000 it wouldn't really make sense to plot them on a linear scale so sometimes a logarithmic scale is used. The only thing you need to do is do log(y) for each value and plot those instead. log should be base 10 by default on a calculator but there will be a button that lets you choose the base

Thank you by the way!

0

reply

Report

#4

(Original post by

So I’d have a regular scale on the y axis. And for each “result” that I have (in this case, size of DNA fragments), I would just stick that value into my calculator and plot whatever I get? Where do “anti logs” come into this because apparently I’m supposed to use it.... :\

Thank you by the way!

**Anonymous**)So I’d have a regular scale on the y axis. And for each “result” that I have (in this case, size of DNA fragments), I would just stick that value into my calculator and plot whatever I get? Where do “anti logs” come into this because apparently I’m supposed to use it.... :\

Thank you by the way!

0

reply

Report

#5

To add to Meowstic's posts, the log (to the base 10) of a value is simply the power of 10 to get that value, for example:

since

so the log of 100 is 2 since you need to 10 squared to get 100.

This is done since the values you have may cover a wide range so it is more practical to use logs of those values instead (so using the example above instead of plotting 0.0001 and 1000000, we can plot instead:

-4, (which is since ),

6, (which is since )).

Is that more clear?

since

so the log of 100 is 2 since you need to 10 squared to get 100.

This is done since the values you have may cover a wide range so it is more practical to use logs of those values instead (so using the example above instead of plotting 0.0001 and 1000000, we can plot instead:

-4, (which is since ),

6, (which is since )).

Is that more clear?

Last edited by simon0; 2 days ago

0

reply

Report

#6

(Original post by

We need to plot the sizes of dna fragments using a log10 base pairs on the y axis. The problem is I have no idea what any of this means. Where do I even start? I tried looking up videos and found some very simplified versions. Then some girl on my course started talking about using "antilogs" and I am extremely confused. If someone could give me a simple introduction to log scales I'd really appreciate it!

**Anonymous**)We need to plot the sizes of dna fragments using a log10 base pairs on the y axis. The problem is I have no idea what any of this means. Where do I even start? I tried looking up videos and found some very simplified versions. Then some girl on my course started talking about using "antilogs" and I am extremely confused. If someone could give me a simple introduction to log scales I'd really appreciate it!

Meowstic & simon0 hopefully have cleared up what's actually happening in a log scaled graph.

0

reply

Report

#7

Thanks guys! That really helped! To clear things up, say if I had a DNA fragment with a size of 4000 base pairs and it moved 20mm down the gel electrophoresis paper, would I just stick the 4000 into my calculator log function and plot that result (3.602...) on the y axis, against the distance on the x axis (so 20mm in this case)?

But when I look up log paper on google, it seems that the y axis scales are all really large, like 100-1000 intervals, so how am I supposed to plot the 3.602?

And still not sure where "exponential" comes in as I've just discovered that I do indeed have to use it. Somehow...?

But when I look up log paper on google, it seems that the y axis scales are all really large, like 100-1000 intervals, so how am I supposed to plot the 3.602?

And still not sure where "exponential" comes in as I've just discovered that I do indeed have to use it. Somehow...?

0

reply

Report

#8

This is an example we were given, it's apparently a semi log graph but I have no idea how. Because if it was, shouldn't the y-axis be non-linear? Sorry the pic is so small and bad quality, it is like that for me too lol, but along the y axis the intervals are 100, 1000 and 10000. Distance along the bottom. Also, as mentioned above the values are really big. That's like if I just didn't use log at all....?

0

reply

Report

#9

Biology is not my speciality but judging by your uploaded image and searching for DNA base pair gel electrophoresis semi-log graphs, I am guessing the y-axis is logarithmic but the y-axis labels are the actual numbers rather than the equivalent log value of the actual value.

(Note on the y-axis, as you go up at every set interval the label is 10 times bigger than the previous value below).

Am I correct in this?

(If not then post away).

(Note on the y-axis, as you go up at every set interval the label is 10 times bigger than the previous value below).

Am I correct in this?

(If not then post away).

0

reply

Report

#10

(Original post by

Biology is not my speciality but judging by your uploaded image and searching for DNA base pair gel electrophoresis semi-log graphs, I am guessing the y-axis is logarithmic but the y-axis labels are the actual numbers rather than the equivalent log value of the actual value.

(Note on the y-axis, as you go up at every set interval the label is 10 times bigger than the previous value below).

Am I correct in this?

(If not then post away).

**simon0**)Biology is not my speciality but judging by your uploaded image and searching for DNA base pair gel electrophoresis semi-log graphs, I am guessing the y-axis is logarithmic but the y-axis labels are the actual numbers rather than the equivalent log value of the actual value.

(Note on the y-axis, as you go up at every set interval the label is 10 times bigger than the previous value below).

Am I correct in this?

(If not then post away).

But yeah seems like the y axis is logarithmic (if my definition of logarithmic as meaning an axis' intervals goes up/down irregularly is correct), but then the next issue is .... why do I have to use the log function if the intervals are as you said, the actual numbers? If it helps, I am supposed to be making a "semi-log graph."

Also, I still have no idea where the exponential is supposed to come in, how I'm supposed to use it etc.....

0

reply

Report

#11

No problems.

The y-axis is still logarithmic but the individual labels have been replaced by the actual values rather than their log values (it is still a semi-log graph but the only difference is the y-axis labels e.g. Instead of label "3", they use label "1000").

Is that better?

The y-axis is still logarithmic but the individual labels have been replaced by the actual values rather than their log values (it is still a semi-log graph but the only difference is the y-axis labels e.g. Instead of label "3", they use label "1000").

Is that better?

Last edited by simon0; 3 hours ago

0

reply

Report

#12

(Original post by

No problems.

The y-axis is still logarithmic but the individual labels have been replaced by the actual values rather than their log values (it is still a semi-log graph but the only difference is the y-axis labels e.g. Instead of label "3", they use label "1000").

Is that better?

**simon0**)No problems.

The y-axis is still logarithmic but the individual labels have been replaced by the actual values rather than their log values (it is still a semi-log graph but the only difference is the y-axis labels e.g. Instead of label "3", they use label "1000").

Is that better?

0

reply

Report

#13

(Original post by

It is! Thank you for your help! So basically, I don’t have to use the log function on my calculator at all?

**Snfkin**)It is! Thank you for your help! So basically, I don’t have to use the log function on my calculator at all?

The only change are just the y-axis labels.

Last edited by simon0; 2 hours ago

0

reply

Report

#14

What I suggest is plot distance (x-axis) against the log of the base pairs (y-axis) and plot all those points.

Then after, change the y-axis labels to their normal numbers (so "2" goes to "100", "3" goes to "1000" etc.).

Then after, change the y-axis labels to their normal numbers (so "2" goes to "100", "3" goes to "1000" etc.).

Last edited by simon0; 2 hours ago

0

reply

Report

#15

(Original post by

What I suggest is plot distance (x-axis) against the log of the base pairs (y-axis) and plot all those points.

Then after, change the y-axis labels to their normal numbers (so "2" goes to "100", "3" goes to "1000" etc.).

**simon0**)What I suggest is plot distance (x-axis) against the log of the base pairs (y-axis) and plot all those points.

Then after, change the y-axis labels to their normal numbers (so "2" goes to "100", "3" goes to "1000" etc.).

0

reply

Report

#16

(Original post by

Thank you so much Just finished my graph

**Snfkin**)Thank you so much Just finished my graph

However, does your graph look fine or can it be confirmed to be done correctly?

0

reply

X

Page 1 of 1

Go to first unread

Skip to page:

### Quick Reply

Back

to top

to top