Finding the electric field at 3 points due to 2 identical charges.

[get_physical]

3 points (a,b and c) and two identical positive charges. How do you find MAGNITUDE of the electric field at the 3 points? I just need to rank them, don't need numbers.

all points are on the x-axis:
A (x=0); charge +Q(x=1); B (x=3); c(x=4); charge+Q(x=5)

(Picture attached in the 3rd post)

Homework Equations

E= (1/4pie) (q/r^2)

The Attempt at a Solution

I just focused on the r^2 since everything in the formula is the same.
for point A: 1^2+ 5^2 = 26
Point B: 2^2+2^2 = 8
Point C: 1^2 + 3+2 = 10

so would B then have the greatest strength while A has the least?

 

[SammyS]

3 points (a,b and c) and two identical positive charges. How do you find MAGNITUDE of the electric field at the 3 points? I just need to rank them, don't need numbers.

all points are on the x-axis:

A (x=0); charge +Q(x=1); B (x=3); c(x=4); charge+Q(x=5)

Homework Equations

E= (1/4pie) (q/r^2)

The Attempt at a Solution

I just focused on the r^2 since everything in the formula is the same.
for point A: 1^2+ 5^2 = 26
Point B: 2^2+2^2 = 8
Point C: 1^2 + 3+2 = 10

so would B then have the greatest strength while A has the least?

r² is in the denominator. You need to add or subtract 1/1² and 1/5², 1/2² and 1/2², etc.

Also you haven't taken into account the direction of the E field from each charge.

 

[get_physical]

Picture attached

 

[get_physical]

Yes, r^2 is the denominator, that's why the smallest r^2 will have the strongest field. Can you please explain what you mean I need to add or subtract?

 

[get_physical]

In that case, would there be no electric field strength at B? since the directions are opposite, so they cancel each other out?

 

[SammyS]

In that case, would there be no electric field strength at B? since the directions are opposite, so they cancel each other out?

Yes.

As for using 1/r, not r²:

1/1+1/5² = 25/25 + 1/25 = 26/25

1/2² + 1/2² = 1/4 + 1/4 = 1/2   (Yes, I know these should be subtracted, but this is just to illustrate the point.)​

 

[get_physical]

Yes.

As for using 1/r, not r²:

1/1+1/5² = 25/25 + 1/25 = 26/25

1/2² + 1/2² = 1/4 + 1/4 = 1/2   (Yes, I know these should be subtracted, but this is just to illustrate the point.)​

In this case, after doing the calculations, would a have the smallest electric field strength since it is -26/25, and then after that would be B with 0 and finally, C?

 

[get_physical]

would you just assume the left is negative while if arrows pointing to the right is positive?
Thanks

 

[SammyS]

In this case, after doing the calculations, would a have the smallest electric field strength since it is -26/25, and then after that would be B with 0 and finally, C?

What do you get for electric field at point C ?

Look at the problem statement. It asks about the "MAGNITUDE of the electric field". (That capitalization was in your original post.)

As with number lines, it's fairly standard to consider a vector pointing to the right to be positive, and left is negative.

 

[get_physical]

Oh ! thank you so much I finally got it. thank you for your patience. appreciated!