The conclusions of Coulomb's experimental work with the torsion balance enabled him to describe the factors that determined the magnitude of the electrostatic force.

 

 

 

Coulomb's law:  the magnitude of the electrostatic force between two charged objects is directly proportional to the product of the two charges on the objects and inversely proportional to the square of the distance of separation between their centres.

 

Coulomb's law can provide insights into the circumstances described in the Get Focused section.

   

Self-Check

Answer the following self-check (SC) question then click the "Check your work" bar to assess your responses.

 

SC 18.  

The illustration shows that the hiker is four times farther from the negative charges in the thundercloud than the people on the observation platform.

  1. Use Coulomb's law to provide a rough comparison of the electrostatic force that would act on a similarly charged strand of hair in each location.

  2. Do you think it is reasonable to assume that a strand of hair would have a similar charge in each location? Explain concisely.

  3. How does your answer to SC 18.b. affect your estimates of forces in SC 18.a.?

   Self-Check Answer

SC 18.

  1. Assuming that the strands of hair in both locations are similarly charged means that distance would be the only difference. Since the distance is four times farther for the hiker, the resulting electrostatic force acting on a strand of hair would be only  th as much for the hiker. This is because the inverse square of a fourfold increase is ( ) 2  or  .

  2. No, it is not reasonable to assume that the strands of hair would have similar charges in each location. The induced charge on a strand of hair for the hiker would be less due to the larger distance of separation between the hair strand and the cloud.

  3. If a strand of hair on the head of the hiker had a smaller induced charge, then the resulting electrostatic force exerted by the charges in the cloud would be even less than the estimate from SC 18.a.