# Electrostatic Issues

2. Three electrically charged particles are placed on a side equilateral triangle d = 40cm as shown below. What is the modulus of force and an outline of the electric force vector acting on charge 3?

To calculate the modulus of force acting on charge 3 we must first calculate separately the influence that loads 1 and 2 have on it, and by both calculate the resulting force.

To calculate the force of repulsion suffered between the two positive charges:

To calculate the force of attraction suffered between the positive and negative charge:

To calculate the resulting force, we apply the cosine law (remembering that each internal angle of an equilateral triangle is 60º, so we must consider an angle of 120º):

In order to outline the direction and direction of the resulting force vector we must remember the repulsion and attraction direction of each force and the parallelogram rule:

3. Four loads are placed on the vertices of a 40cm and 30cm sides rectangle, as shown in the figure below:

How strong is the force felt in particle 4?

To calculate the resulting force at the point where particle 4 is located, we must first calculate each of the electric forces acting on it.

For the force of particle1 acting on 4:

For the force of particle2 acting on 4:

For the force of particle3 acting on 4:

To calculate the resulting force:

In order to outline the direction and direction of the resulting force vector we must remember the repulsion and attraction direction of each force and the parallelogram rule:

As in the modulus of forces calculation, we cannot sum all the vectors at once, so in parts:

## Electric field

1. An electric field is generated by a positive point charge. At a distance of 20cm a charge test particle q = -1µC is set, being attracted by the field, but an external force of 2N causes the charge to balance, as shown in the figure:

What should be the field generating load module for this to be possible?

To do this calculation we use the relation:

However the problem does not say what the intensity of the electric field is, but F being the force necessary for the described system to be in equilibrium:

Substituting in the first equation:

## Electric potential

1. An electric charge of intensity Q = + 7µC generates an electric field in which two points are represented, A and B. Determine the work done by the force to carry a charge. from point to point (B to A), given the figure below:

First we need to calculate the electric potential at each point through the equation:

In A:

In B:

Knowing these values, we simply apply to the work equation of an electric force: