What is the equation for calculating the electric field and charges?

[johnhunk]

Homework Statement

http://imageshack.us/photo/my-images/94/mphelp.jpg/"

Homework Equations

coulomb law

The Attempt at a Solution

no idea.. maybe other E field is -0.3 to cancel it out?

 

[Tomer]

Are you talking about part 1 or 2?
Are you trying to calculate the field at point A?

In that case, are you used to working with the coulomb law in it's vector form? It'll be much easier working in this form, with this formula:
The field E inflicted by a point charge q situated at point A on point B is:
$\vec{E} = \frac{kq}{d^{3}}\vec{AB}$

where d is the distance between A and B and K is the Coulomb constant.
Writing everything in vector form should be pretty simple.

If you're totally unfamiliar with the vector form, you have no choice but to calculate separately the x and y components of the electrical field at the point A from the two different charges. That would be 4 different calculations involving trigonometry and is pretty tiring.

If you're still stuck you'll get further help, but give it a fair try first.

Btw the x fields might cancel out and might not. You have to calculate it - it isn't trivial, since the charges aren't equal and so aren't the distances between them and point A.

Good luck!

 

[johnhunk]

i mean part b.

 

[Tomer]

According to your solution, there's a field acting both on the y and on the x axes. A charge located at point B would not be able to cancel out the x field, only the y field.

If I read something wrong and there was no x field cause it canceled out, what you said is of course right - you need exactly the same y field in the opposite direction. You know the expression for an electrical field, use it to get q.

 

[rwisz]

The equation for calculating the electric field is E = k * Q / r^2, where E is the electric field, k is the Coulomb's constant (8.99 x 10^9 N * m^2 / C^2), Q is the charge of the object, and r is the distance between the object and the point where the electric field is being measured.

To calculate the charges, you can rearrange the equation to Q = E * r^2 / k. This equation allows you to determine the charge of an object if you know the electric field and the distance from the object.

It is important to note that this equation only applies to point charges and can be used to calculate the electric field and charges for multiple point charges by using the principle of superposition. Additionally, this equation assumes that the charges are stationary and do not create a changing magnetic field. In cases where there is a changing magnetic field, the full equation for the electric field, known as Maxwell's equation, must be used.