Determining the magnitude of the charge (Coulombs Law)

[meeklobraca]

Homework Statement

Two equal charges exert an electric force on each other of 0.0385N when positioned 0.15 m apart. Determine the magnitude of the charge on each point.

Homework Equations

Fe=Kq1q2/R^2

The Attempt at a Solution

I narrowed it down to

q1q2=FeR^2/K

q1q2=96357.0634C^2

I squared this and I get q1q2=310.4143415C

This is not the answer to the question. I am close as far as the numbers go but I am not sure what I am missing here.

 

[LowlyPion]

Homework Statement

Two equal charges exert an electric force on each other of 0.0385N when positioned 0.15 m apart. Determine the magnitude of the charge on each point.

Homework Equations

Fe=Kq1q2/R^2

The Attempt at a Solution

I narrowed it down to

q1q2=FeR^2/K

q1q2=96357.0634C^2

I squared this and I get q1q2=310.4143415C

This is not the answer to the question. I am close as far as the numbers go but I am not sure what I am missing here.

Could be the number of significant digits.
Could be that the charges could either both be plus or minus, but they do only ask for magnitude.

 

[meeklobraca]

The answer given is 3.1 x 10-7 C

The answer I got was 3.1 x 10^2C right? So I figure the numbers are correct, just something missing, or maybe even the answer in the book is wrong.

 

[LowlyPion]

The answer given is 3.1 x 10-7 C

The answer I got was 3.1 x 10^2C right? So I figure the numbers are correct, just something missing, or maybe even the answer in the book is wrong.

Recalculate it again then. (K is 9*10⁹ And you are dividing by it.)

 

[meeklobraca]

yeah, that's been done.

 

[LowlyPion]

yeah, that's been done.

If you divided by 10⁹ and you got 10² ... that's a lot of 10's to be off.

Why don't you type out your whole calculation?

On the face of it you have 10^-2*10^-1*10^-1/10⁹

10² seems like an unlikely result.

 

[meeklobraca]

I have here

qq=0.0385N x (0.15)(0.15) / 8.99x10^9

So I get

8.66x10-4 / 8.99x10^9

 

[LowlyPion]

I have here

qq=0.0385N x (0.15)(0.15) / 8.99x10^9

So I get

8.66x10-4 / 8.99x10^9

And that gives 9.62 x 10^-14

And taking the square root ...

 

[meeklobraca]

"And that gives 9.62 x 10-14"

I wish I could copy and paste what my calculator is saying because I just don't get that answer.

 

[meeklobraca]

I tried it with an oline calculator and I got what you got, so I am not sure if the settings on my calculator are just messed up.

 

[LowlyPion]

I tried it with an oline calculator and I got what you got, so I am not sure if the settings on my calculator are just messed up.

Nothing like pencil and paper.

If in doubt, work it out.

 

[meeklobraca]

Its been a while since I've done that. How do you divide exponents? Can you give me a quick crash course?

 

[LowlyPion]

Its been a while since I've done that. How do you divide exponents? Can you give me a quick crash course?

Just look at post 6:
https://www.physicsforums.com/showpost.php?p=1924414&postcount=6

Dividing by 10 makes it 10^-1

Dividing by 10⁹ makes it 10^-9

Dividing by exponents subtracts. Multiplying adds.

Don't let your teacher know you didn't know.

 

[meeklobraca]

OK see there we go.

I have 8.66x10-4 / 8.99x10^9 right?

Im taking 8.66x10^+4 and dividing it by 8.99x10^+9

But if I am dividing an exponent I am supposed to make the +9 a negative 9?

 

[LowlyPion]

OK see there we go.

I have 8.66x10-4 / 8.99x10^9 right?

Im taking 8.66x10^+4 and dividing it by 8.99x10^+9

But if I am dividing an exponent I am supposed to make the +9 a negative 9?

That should be -4 and dividing by 10⁹ makes that 10^-13 and the numerator being less than denominator makes it 9.xx * 10^-14.

 

[meeklobraca]

That was a typo on my part.

That makes perfect sense, I still don't get though why my calculator spits out 96329.25473

This is on a TI83 sci. calulator

8.6610^(-4)/8.9910^(9)

96329.25473

 

[LowlyPion]

That was a typo on my part.

That makes perfect sense, I still don't get though why my calculator spits out 96329.25473

This is on a TI83 sci. calulator

8.6610^(-4)/8.9910^(9)

96329.25473

I'd recommend not using that calculator to figure orbital trajectories for a Mars landing then.

Maybe use it for grocery shopping?

 

[meeklobraca]

its going to be used as a stool for my radio here if it doesn't smarten up.