**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:*