# Equator and perpendicular bisector

1. Apr 24, 2015

### gracy

The pointed line is equator as well as perpendicular bisector.Right?

2. Apr 24, 2015

### mathman

It looks like the perpendicular bisector of the triangle. I have never seen the term equator with reference to a triangle.

This question belongs in the math forum.

3. Apr 24, 2015

### gracy

No.Actually I was learning electric field along equatorial line.

4. Apr 24, 2015

### nasu

Equatorial line of what? Of the Earth?

5. Apr 24, 2015

### gracy

No.Equatorial line of the attached image.

6. Apr 24, 2015

### gracy

look at figure 18.5

7. Apr 24, 2015

### nasu

What is the context?
You may call it equatorial line, if you use some more general meaning of the word.
Is this a translation from another language?

The important thing is what is that line? What properties does it have? And again, context.

8. Apr 24, 2015

### gracy

I am sorry but what are you referring to?

9. Apr 25, 2015

### Staff: Mentor

That is an unusual use of the word; the author is using some imagery here to relate the sphere to the Earth.

EDIT: see later correction
The problem involves a charged sphere. The equator doesn't relate to the triangle directly, it relates to the positioning of the line charge. Picture the line charge as lying along the equator of the charged spherical shell under consideration. Distance L is marked on that equatorial line. (Assuming I'm understanding it correctly.)

Last edited: Apr 26, 2015
10. Apr 25, 2015

### nasu

Where do you see the reference to a charged sphere? I only see a line of charge.
But it is not clear, the image should show more than it does.

11. Apr 26, 2015

### Staff: Mentor

The figure 18.5 that gracy attached does not refer to a sphere at all. I think the person who wrote the text is a non-native speaker of English (from India, by the looks of it), and therefore made a poor choice of words. Or maybe Indian English does indeed regularly use "equatorial" in this sense.

I think it's clear from the diagram that "equatorial line" here means what American and British English speakers call "perpendicular bisector."

12. Apr 26, 2015

### Staff: Mentor

I believe jtbell has the right grasp of the situation.

There seem to be are a number of problems with the text. The major one being the use of the word "equatorial" in association with a line charge. I can only find the word equatorial to be defined* in association with a dipole (equal point charges of opposite polarity). I can't find another reference where the word "equatorial" is associated with any other charge distribution, certainly not a line charge because it seems clear that a line charge loses any analogy with Earth and its pair of opposite poles. Perpendicular bisector is the term that should be used.

* http://www.physics4all.org/XII/Ch_1/img_14.gif [Broken]

Last edited by a moderator: May 7, 2017