Calculating Electrostatic Force Between Charges

[nopescope]

Hi all. I don't know if I'm completely over thinking this question or just not getting it. Please tell me if I'm correct.

A -8.0μC charge is located 0.30m to the left of a +6.0μC charge. What is the magnitude and direction of the electrostatic force on the positive charge?

F=KQaQb/r^2

F=(9x10^9)(-8.0x10^-6)(+6.0x10^-6)/(0.30m)^2 = -4.8N...so answer is 4.8, to the right.

So, I think that because the F is -4.8 means that the direction is going to the right because a negative means that it is an attractive force and the +6 charge will be attracted to the -8 charge. Am I correct?

 

[Doc Al]

Ask yourself: Do the charges attract or repel? Given that answer, in what direction must the force act?

 

[nopescope]

The -8 and +6 will attract because they are opposite charges. So, the positive charge will go to the right.

 

[Doc Al]

The -8 and +6 will attract because they are opposite charges.

Right, they will attract.

So, the positive charge will go to the right.

Why? If they attract, the force on the positive charge must be towards the negative charge.

 

[nopescope]

Oh, I see. I think drawing a picture of the charges would have helped. So, because the -8 is to the left of the +6, they are attracted to each other the +6 will move to the left towards the -8.

I was originally just looking at the "left" in the question and automatically assuming, "ok, then it has to go right."

Thanks Doc

 

[nopescope]

Also, does the amount of charge have an affect on the direction of the force? For example...say there was a -4 charge located to the left of a +6 charge...would that still be moving to the left?

 

[Doc Al]

Also, does the amount of charge have an affect on the direction of the force?

No, just the signs.

For example...say there was a -4 charge located to the left of a +6 charge...would that still be moving to the left?

Sure. The charges have opposite signs, so they attract.

(Of course, if there are more than 2 charges involved, you'll need to figure out the net force on any particular charge.)

 

[nopescope]

Thank you so much! I actually get it now. My teacher was confusing me.