Where would you place a proton to produce this field at the origin?

[cowmoo32]

Homework Statement

You want to create an electric field = < 0, 5e4,0 > N/C at location < 0, 0, 0>.
Where would you place a proton to produce this field at the origin?

Homework Equations

$$\vec E = q\hat{r} / 4\pi\varepsilon r^2$$

The Attempt at a Solution

I'm not sure how to treat $$\hat{r}$$ in the equation. Obviously, I know it's equal to r/rmag, but rmag is what's throwing me.

 

[LowlyPion]

Homework Statement

You want to create an electric field = < 0, 5e4,0 > N/C at location < 0, 0, 0>.
Where would you place a proton to produce this field at the origin?

Homework Equations

$$\vec E = q\hat{r} / 4\pi\varepsilon r^2$$

The Attempt at a Solution

I'm not sure how to treat $$\hat{r}$$ in the equation. Obviously, I know it's equal to r/rmag, but rmag is what's throwing me.

An electric field is a vector field. So where you place the proton will determine both the magnitude and the direction of the electric field.

 

[Doc Al]

I'm not sure how to treat $$\hat{r}$$ in the equation. Obviously, I know it's equal to r/rmag, but rmag is what's throwing me.

That's just a unit vector (magnitude = 1) giving the direction of the field. The field from a positive charge is radially outward.

 

[cowmoo32]

Ok, I thought that unit vector might be 1, so I solve for $$r^2$$, correct? I tried that and didn't get the right answer.

 

[LowlyPion]

Ok, I thought that unit vector might be 1, so I solve for $$r^2$$, correct? I tried that and didn't get the right answer.

What values did you use?

 

[cowmoo32]

5e4 = [(1.6e-19)(9e9)] / r^2

I got r = 1.69707e-7

 

[LowlyPion]

5e4 = [(1.6e-19)(9e9)] / r^2

I got r = 1.69707e-7

Why do you think this is incorrect?

 

[cowmoo32]

Because when I submit it online it tells me that's the wrong answer. I'm not sure what I'm doing wrong.

 

[LowlyPion]

Because when I submit it online it tells me that's the wrong answer. I'm not sure what I'm doing wrong.

Is it possible it's your coordinates for placing the proton? They are asking you where you would place the proton to affect this electric field vector at 0,0,0.