Find the magnitude of the electric field at point P

In summary, two identical spheres with the same charge at the vertices of an equilateral triangle will exert an outward electric field at point P. The horizontal force components are equal and opposite, resulting in a net electric field of 6910 N/C. The mistake in the calculation was taking the wrong distance between P and the midpoint between the two charges, resulting in an incorrect answer. The correct answer is B, with a net electric field of 5196 N/C.
  • #1
paulimerci
287
47
Homework Statement
Question posted below.
Relevant Equations
E = kq/r^2
There are two identical spheres with the same charge that are the vertices of an equilateral triangle. ##+3 \mu C## will exert an outward electric field, which is drawn in the FBD below (see the attached pic), Since the horizontal force components (1x and 2x) are equal and opposite at point P, we can cancel those two vectors, and the remaining y component vectors will give the resultant magnitude of the electric field at point P.
$$ E = \frac {kq}{r^2}$$
$$ E_{1y} = \frac {8.99 \times 10^9 \times 3 \times 10^-6 sin 60} {6.76}$$
$$ E_{1y} = 3455 N/C$$

$$E_{2y} = \frac {8.99 \times 10^9 \times 3 \times 10^-6 sin 60} {6.76}$$
$$ E_{2y} = 3455 N/C$$
$$ E _{net} = 6910 N/C$$
I'm not sure where I made a mistake because none of the answers match my answer. Can anyone point out where my mistake is?
 

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  • #2
What does r represent in your relevant equation? Think.
 
  • #3
haruspex said:
What does r represent in your relevant equation? Think.
r is the distance between the charge and the reference point (P).
 
  • #4
paulimerci said:
r is the distance between the charge and the reference point (P).
I see where I did a mistake I took the wrong distance (between P and the midpoint between two charges). r=3m, Is ##E_{1y} + E_{2y} = 2598+2598 = 5196 N/C##. So the answer choice is B?
 
  • #5
paulimerci said:
I see where I did a mistake I took the wrong distance (between P and the midpoint between two charges). r=3m, Is ##E_{1y} + E_{2y} = 2598+2598 = 5196 N/C##. So the answer choice is B?
Looks right.
 
  • Like
Likes paulimerci
  • #6
haruspex said:
Looks right.
Thank you!
 

1. What is the definition of electric field?

The electric field is a physical quantity that describes the strength and direction of the force exerted on a charged particle by other charged particles in its vicinity.

2. How is the magnitude of the electric field at point P calculated?

The magnitude of the electric field at point P can be calculated using the formula E = kQ/r^2, where k is the Coulomb's constant, Q is the charge of the source particle, and r is the distance between the source particle and point P.

3. What factors affect the magnitude of the electric field at point P?

The magnitude of the electric field at point P is affected by the charge of the source particle, the distance between the source particle and point P, and the medium in which the particles are located.

4. How does the direction of the electric field affect the magnitude at point P?

The direction of the electric field at point P is perpendicular to the electric field lines and is dependent on the direction of the source particle's charge. The magnitude of the electric field is not affected by its direction.

5. Can the magnitude of the electric field at point P be negative?

Yes, the magnitude of the electric field at point P can be negative. This indicates that the direction of the electric field is opposite to the direction of the source particle's charge.

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