# Homework Help: Electic field question - geometry

1. Apr 23, 2005

### flythisforme

I have a problem where I need to find the net electric field on a point due to 6 charges. I attached the diagram. It is a pentagon of 5 charges with a 6th charge in the center. Each side of the pentagon is 4 mm, and there is a point P on the center of one side. I found that the line from point P to point 1 of the pentagon is 4.99mm, using the law of cosines. I need to figure out what the angle is at point P from the line to the side of the pentagon (the one I marked with a question mark), so I can find the x and y components of this line. I am not sure if the line bisects the 54° angle at point 1. Can someone help me with this?

Thanks a lot. I really appreciate it.

#### Attached Files:

• ###### pentagon.JPG
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2. Apr 23, 2005

### whozum

Are you trying to find the field at point P? All the x components cancel by symmetry..

3. Apr 23, 2005

### flythisforme

Yeah, but I need the angle there to find the y component of it.

4. Apr 23, 2005

### whozum

If line P to 1 is 5, then use the law of sines.

$$\frac{sin(a)}{A} = \frac{sin(b)}{B}$$