Coulomb’s law
Answers are for parents and teachers.
1
Charges of 4 µC and 3 µC are 6 cm apart in a vacuum. With what force (N) do they interact?
30
2
Two spheres with equal charges repel each other with 0.9 N at 10 cm. Find the charge.
q² = 0.9 · 0.01 : 9·10⁹ = 10⁻¹² C², q = 10⁻⁶ C = 1 µC.
3
The distance between two charges is reduced from 2 cm to 1 cm. By what factor does the force change?
It increases 4 times.
4
Identical spheres carry +9 µC and –3 µC. After touching and separating, what is each sphere’s charge in µC?
3
5
In the torsion-balance experiment, why does touching a charged sphere with an identical uncharged one split the charge equally? How did Coulomb use this to reduce the charge?
Because the spheres are identical, the charge shares equally; Coulomb reduced the charge by 2, 4, 8 times to test the dependence of force on the product of charges.