Find the electric force on a point charge

In summary, the forces on charge q2 are -3.83 x 10-2 N and Fx = 3.83 x 10-2 N, while the forces on charge q1 are 8.99 x 10^9 N and Fy = 0.
  • #1
henrco
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Homework Statement


A point charge q1 = 4.40 μC is at the origin and a point charge q2 = 6.00 μC is on the x axis at x = 2.49 m.
i) Find the electric force on charge q2
ii) Find the electric force on charge q1

Homework Equations


Coulomb's law F = k (q1q2)/d^2

The Attempt at a Solution


Part i)
Using k = 8.99 x 10^9, q1 = 4.40 x 10^-6, q2 = 6.00 x 10^-6 and d = 2.49m
Plug these values into the equation

F = (8.99 x10^9) x (4.40 x 10^-6) x (6.00 x 10^-6)/ (2.49)^2
F = 3.83 x 10^-2 N

Checked this value a couple of times and seems correct.

Part ii)
Since we are looking for the force from q2 to q1, it is the same magnitude but opposite in direction.

F = -3.83 x 10^-2 N

I'm a little unsure of this, but if feels correct. If I'm wrong, any guidance welcome.
 
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  • #2
Your work looks correct. But I wouldn't use a minus sign to indicate the direction of the force in part (ii). If you want to specify the directions of each force, then it would be better to use a descriptive phrase such as "toward the other charge" or "away from the other charge".

[If you are dealing with components of a force, such as the x-component or the y-component, then you could have a negative component. But this would require having a clearly stated coordinate system in which the directions of positive x and positive y are known.]
 
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  • #3
Thanks for your reply.

TSny said:
[If you are dealing with components of a force, such as the x-component or the y-component, then you could have a negative component. But this would require having a clearly stated coordinate system in which the directions of positive x and positive y are known.]

"A point charge q1 = 4.40 μC is at the origin and a point charge q2 = 6.00 μC is on the x axis at x = 2.49 m. "
From the question(extract above) it specifies the forces along the x-axis, so I would take these to be the x-components of the forces.

Therefore should I quote the minus sign for the answer to part ii) ?
 
  • #4
In this case I would give the direction of the force in (i) as "toward the positive x direction",
or I would state the answer as Fx = 3.83 x 10-2 N, Fy = 0. (Also, Fz = 0 if you usually work in 3 dimensions of space.)

Similarly for (ii) I would give the direction of the force as "toward the negative x direction",
or I would state the answer as Fx = -3.83 x 10-2 N, Fy =0. But I would still not state the answer as F = -3.83 x 10-2 N.
 
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Related to Find the electric force on a point charge

What is the formula for calculating the electric force on a point charge?

The formula for calculating the electric force on a point charge is F = k * (Q1 * Q2) / (r * r), where k is the Coulomb's constant, Q1 and Q2 are the charges of the two point charges, and r is the distance between the two charges.

How do I determine the direction of the electric force on a point charge?

The direction of the electric force on a point charge is determined by the direction of the electric field at the point charge. The electric field points away from positive charges and towards negative charges.

What is the unit of measurement for electric force?

The unit of measurement for electric force is Newtons (N).

Can the electric force on a point charge be negative?

Yes, the electric force on a point charge can be negative. This indicates that the force is attractive, meaning the two charges are of opposite sign.

How does distance affect the electric force on a point charge?

The electric force on a point charge is inversely proportional to the square of the distance between the two charges. This means that as the distance increases, the force decreases. Conversely, as the distance decreases, the force increases.

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