In the Rutherford model of hydrogen the electron (mass=9.11x10-31 kg) is in a planetary type orbit around the proton (mass=1.67x10-27 kg). Assume that the radius of the orbit is 2.5 Angstroms (10-10 m). (a) What is the magnitude of the gravitational force of attraction between electron and proton? AN (b) What is the magnitude of the electric force of attraction between electron and proton? N

(a)

(b)

Explanation:

(a) We use Newton's law of universal gravitation, in order to calculate the gravitational force between electron and proton:

Where G is the Cavendish gravitational constant, and are the masses of the electron and the proton respectively and r is the distance between them:

The minus sing indicates that the force is repulsive. Thus, its magnitude is:

(b) We use Coulomb's law, in order to calculate the electric force between electron and proton, here k is the Coulomb constant and e is the elementary charge:

Its magnitude is:

the duration of a photographic flash is related to an rc time constant, which is 0.100 μs for a certain camera.