Can you please help me in this question? Help would be REALLY appreciated :) An unknown material has a refractive index of 2.78 x106. How fast is light traveling in in this material?

Answerboth technicians (a) and (b);

Answerthe force between the charges will be  f/9 (one-ninth of force f)explanationcoulomb's law relates the magnitudes  two point charges q₁ and q₂, the distance, r, between the charges, and the electrostatic force, f, between the two charges:     k represents coulomb's constant, k = 8.99×10⁹ n·m²/c².note that if we have r = 3r, then   

Imma say go with a (:

C) the periods  of day and night would be fixed all year for anyone at the  equator