A small doubt about electric flux

AI Thread Summary
Electric flux is a scalar quantity that can be positive or negative, depending on the direction of the electric field relative to the surface area. The confusion arises from the interpretation of negative flux, which is not smaller in magnitude than positive flux; it simply indicates the direction of flow. In the examples discussed, the book's terminology regarding "higher" or "lower" flux likely refers to magnitude rather than the sign of the flux. Clarification suggests that negative flux is equivalent in amount to positive flux, just directed differently. Understanding this distinction resolves the doubts about comparing flux values in the given scenarios.
Joe Da Bro
Messages
4
Reaction score
0
Hey there...
As far as I know, electric flux is a scalar quantity which means that negative values are smaller than zero. This concept really confuses me since most of the exercises I dealt with suggest that negative flux somehow is larger than zero flux

Example 1
yf_Figure_22_32.jpg

the uniform field is directed to the right, which surface has the lower electric flux?
is it S1 which is negative or S2/S4/S5/S6 ( that's the correct answer according to my book)?

Example 2
https://lh6.ggpht.com/f3KBE_uxMhA2zCSgcxfdIu26-n0OOGrOHNwK7lQxsSYGp__YJLIWuP7uSkZUBVLUFpwJQw=s170
Which surface has the lower electric flux?
is it S2 which is negative or S1 which is zero ( that's the correct answer according to my book) ?

So is the problem with me or with the book itself or what exactly?
Thanks in advance.
 
Last edited:
Physics news on Phys.org
Welcome to PF;
The amount of flux passing through a surface is a scalar - not the flux itself.
The flux may be positive or negative depending on which way it flows through the surface.
 
Simon Bridge said:
Welcome to PF;
The amount of flux passing through a surface is a scalar - not the flux itself.
The flux may be positive or negative depending on which way it flows through the surface.

Isn't the flux itself a dot product? which also means it's scalar too. care to elaborate please?
Thanks for your reply...
 
A dot product of what with what?
Think of the flux as the amount of flow.
 
Simon Bridge said:
A dot product of what with what?
Think of the flux as the amount of flow.

the electric field and the vector area
 
Backtrack - I think I can see a way through for you.
This is just like the component of the velocity vector in the x direction of interest is given by a dot product (##\vec v \cdot \hat i##), which will give a scalar, which may be positive or negative; but a negative speed is no slower than a positive speed. Similarly a negative flux is the same amount of flux as a positive flux, it's just headed into the volume rather than out of it ... and that is an arbitrary choice: it is just as good to define positive in and negative out.
 
Simon Bridge said:
Backtrack - I think I can see a way through for you.
This is just like the component of the velocity vector in the x direction of interest is given by a dot product (##\vec v \cdot \hat i##), which will give a scalar, which may be positive or negative; but a negative speed is no slower than a positive speed. Similarly a negative flux is the same amount of flux as a positive flux, it's just headed into the volume rather than out of it ... and that is an arbitrary choice: it is just as good to define positive in and negative out.

that's what I wanted .. I am really thankful, just to make sure, negative flux>zero flux in both examples? if so then, all the doubt will vanish.. Thanks again!
 
I think when your book asks about "higher" or "lower" they are referring to the magnitude (absolute value) of the flux. As a native English speaker, I personally would say "larger" or "smaller", instead, because that implies magnitude. Is this an English-language textbook, or are you trying to translate from some other language? Or maybe the book was written by a non-native English speaker.
 
Back
Top