# Homework Help: What is the Strength of the Electric Field?

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1. Mar 14, 2015

### littlejon

1. The problem statement, all variables and given/known data
Specify the strength of the electric field. Let r = 7.3cm .

2. Relevant equations
E1= (k*p)/(r^2+a^2)^3/2
Here k= constant used in Coulomb's law. a= half the length of dipole
p= dipole moment = charge x length of dipole. Charge = 3nC and length of dipole

3. The attempt at a solution
E1= (9E9)(3E-9)/(.146)^2+(.073)^2)^(3/2)= 6207

I got this wrong, but does anyone have any advice on how to solve this?

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Last edited: Mar 14, 2015
2. Mar 14, 2015

### SammyS

Staff Emeritus
It appears that you used the amount of charge for p, rather than dipole moment.

$p=2aq$

3. Mar 14, 2015

### littlejon

Then ((9E9)(2*.073*3E-9))/((.146^2)+(.073)^2)^(3/2) = 906?

4. Mar 14, 2015

### SammyS

Staff Emeritus
I'm surprised that a problem like this would have a be larger than r. Usually it's the other way around.

What is the complete problem you were given to solve? -- word for word.

5. Mar 15, 2015

### littlejon

What are the strength and direction of the electric field at the position indicated by the dot in the figure (Figure 1) ?
Specify the strength of the electric field. Let r = 7.3cm .
Express your answer using two significant figures.
Thats word for word.

6. Mar 15, 2015

### SammyS

Staff Emeritus
In the figure, the charges have a separation, 2r . That is to say, a = r .

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