Xploring Coulomb’s

WHAT I KNEW?

Honestly speaking i lack knowledge about this law but as far as i know we’ve already touched this lesson during our junior high school days but I can’t really remember.

WHAT I LEARNED?

Through the work of scientists in the late 18th century, the main features of the electrostatic force—the existence of two types of charge, the observation that like charges repel, unlike charges attract, and the decrease of force with distance—were eventually refined, and expressed as a mathematical formula. The mathematical formula for the electrostatic force is called Coulomb’s law after the French physicist Charles Coulomb (1736–1806), who performed experiments and first proposed a formula to calculate it.Coulomb’s Law

F=k\frac{|{q}_{1}{q}_{2}|}{{r}^{2}}.
k=8\text{.}\text{988}×{\text{10}}^{9}\frac{\text{N}\cdot {\text{m}}^{2}}{{\text{C}}^{2}}\approx 8\text{.}\text{99}×{\text{10}}^{9}\frac{\text{N}\cdot {\text{m}}^{2}}{{\text{C}}^{2}}.

The electrostatic force is a vector quantity and is expressed in units of newtons. The force is understood to be along the line joining the two charges.

According to Coulomb, the electric force for charges at rest has the following properties:

  1. Like charges repel each other; unlike charges attract. Thus, two negative charges repel one another, while a positive charge attracts a negative charge.
  2. The attraction or repulsion acts along the line between the two charges.
  3. The size of the force varies inversely as the square of the distance between the two charges. Therefore, if the distance between the two charges is doubled, the attraction or repulsion becomes weaker, decreasing to one-fourth of the original value. If the charges come 10 times closer, the size of the force increases by a factor of 100.
  4. The size of the force is proportional to the value of each charge. The unit used to measure charge is the coulomb (C). If there were two positive charges, one of 0.1 coulomb and the second of 0.2 coulomb, they would repel each other with a force that depends on the product 0.2 × 0.1. Thus, if each of the charges were reduced by one-half, the repulsion would be reduced to one-quarter of its former value.

NOTE:

  • The Coulomb force is extraordinarily strong compared with the gravitational force, another basic force—but unlike gravitational force it can cancel, since it can be either attractive or repulsive.
  • The electrostatic force between two subatomic particles is far greater than the gravitational force between the same two particles.

HOW I LEARNED?

Really Physics is not that easy, there are a lot of courage and determination to better understand the lessons. It is true that we should understand first what is in the problem and what does the problem asking for. Through the help of Sir Lex and of course my classmates who understand the lesson first, I’ve got the chance to asked how did they come up with that answer, what is the formula to be used, and many more for me to better understand the lesson.

For example:

Two point-like charges carrying charges of +3×10−9 C and −5×10−9 C are 2 m apart. Determine the magnitude of the force between them and state whether it is attractive or repulsive.

Given:

  • Q1 = +3×10−9 C
  • Q2 = −5×10−9 C
  • r = 2 m

We know that k=9,0×109 N·m2·C−2.

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Determine the magnitude of the force

Using Coulomb’s law we have

F=k (Q1Q2)/r2=(9,0×109)(3×10−9)(5×10−9)(2)2=3,37×10−8 N

Thus the magnitude of the force is 3,37×10−8 N. However since the point charges have opposite signs, the force will be attractive.

Free body diagram

We can draw a free body diagram to show the forces. Each charge experiences a force with the same magnitude and the forces are attractive, so we have:

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REFLECTIONI

This lesson is not really easy to understand, there are a lot of courage and willingness to learned in order to understand this lesson. Friends are really sometimes our heroes because of them I’ve got a helping hand of course also with our teacher. 

I can relate this to the challenges in life, we encounter different obstacles in life but we must always have the will to find a solution.