# Homework Help: Electric field Question

1. Sep 6, 2015

### ToonBlue

1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

This is problem I have found online and this is the part I don't understand how they come up with this.

How did they get this for the x component since y component cancel out due to being symmetry ?

Last edited: Sep 6, 2015
2. Sep 6, 2015

### Antonius

I think they are trying to find dE not E...

3. Sep 6, 2015

### ToonBlue

The above is the formula given in my lecture note .

In the solution provided in the problem , it is given as which means that is the unit direction of the component.

In this case , since there is no y component (symmetry) , it has only x component but how do they get ?

4. Sep 6, 2015

### Antonius

The y component will cancel out I think when you take the Integral over all points towards point O. I believe the formula ( at the end ) provided in the solution is trying to calculate the dE at point O.
Wait for more qualified members to reply. I am taking Electricity and Magnetism course right now :)

5. Sep 8, 2015

### Staff: Mentor

The diagram in your first post shows you dE; it's the field you'll see at O due to the charge contained in the short length, dl. The electric field at any point has both a magnitude (illustrated by the arrow having a length) and a direction (shown by the angle of arrow dE to the reference axes).

It's not until you sum the fields due to multiple fragments of charge will you see cancellations, this entails integrating dE for all of the line charge.

6. Sep 8, 2015

### rude man

The y component cancels out only after you have integrated dE.

7. Sep 25, 2015

### ToonBlue

May I know why does the dE point away and not toward the dL?

8. Sep 25, 2015