ELECTRIC FORCE


 1. Definition
 Electric force is the attractive force or the repulsion force between two charges of the same or opposite type where the force is directly proportional to the sum of the two charges and inversely proportional to the square of the distance.

2. Formula and Example
Where:
  • F is the electric force (N)
  • q1 and q2 are the signed magnitudes of the charges (C)
  • r is the distance between the charges (m)
  • k is the Coulomb's constant 9×109 Nm2·C−2
Example:
 A positive charge q exerts a force of magnitude -0.20 N on another charge -2q. Find the magnitude of each charge if the distance separating them is equal to 50  cm.

Solution:

F = k (q) ( - 2q) / r2 , r = 0.5 m , F = - 0.20 N ,

- 0.2 = - 2 q2 k / 0.52

q2 = 0.2 × 0.52 / (2 k)

q = √ [ (0.2 × 0.52 / (2 × 9 × 109) ] = 1.66 × 10-6 C

q = 1.66 × 10-6 C , -2 q = -3.23 × 10-6 C 

3. Important Figure

 Born on June 14, 1736, in Angoulême, France, Charles-Augustin de Coulomb studied engineering and plied his trade with the military before winning accolades for his work in torsion balances. He offered pioneering theories in the force found between electrical charges, as well as magnetic attraction and repulsion. The unit of measurement known as the coulomb is named in his honor. He died in Paris on August 23, 1806.

 Charles de Coulomb enrolled in military school in 1759, graduating from the Royal Engineering School of Mézières (École royale du génie de Mézières) in 1761. Early in his career, Coulomb worked in structural design and soil mechanics. Over the next 20 years, he was stationed in a number of locations. Beginning in 1764, he served nine years in Martinique, West Indies, and was in charge of building Fort Bourbon.
 After falling ill with fever, in 1773, Charles de Coulomb returned to France and began some of his most important work on applied mechanics. That same year, he presented his first scholarly paper, "Statistical Problems applied to Architecture," to the Académie of Sciences. His use of calculus to overcome various discrepancies in engineering issues highly impressed the Académie.
 In 1779, Charles de Coulomb was sent to Rochefort, France, to supervise the construction of a fort made entirely of wood. During this time, Coulomb used the shipyards at Rochefort for his research on friction and the stiffness of ropes. These experiments led to his major work, Theorie des Machines Simples ("Theory of Simple Machines"), in 1781, which won him the Grand Prix of the Académie of Sciences.


4. Examples in Everyday Life
 One example of an electric force is the lightning we see in a thunderstorm. Electric force can also be seen in everyday life through the electromagnetic forces that enable magnetism,  such as tthat in refrigerator magnets. Batteries are another everyday example of an electric force, using direct electric currents to charge devices such as mobile phones. One especially common example of electric force is the wattage needed to illuminate a lightbulb. Another example is the electric stove which transfers electrical energy into heat through resistive coils, halogen lamps or electrical induction.



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