#### The planetary model of the atom pictures electrons orbiting the atomic nucleus much as planets orbit the Sun. In this model, you can view hydrogen, the simplest atom, as having a single electron in a circular orbit 1.06×10^{-10} m in diameter.

#### (a) If the average speed of the electron in this orbit is known to be 2.20×10^{6} m/s, calculate the number of revolutions per second it makes about the nucleus.

#### (b) What is the electron’s average velocity?

## Solution:

### Part A

The formula to be used is

Rearraging the formula–solving for the distance

Substituting the given values

We know the total distance traveled in 1 sec. We know that in 1 revolution, the total distance is

Therefore, the total number of revolutions traveled in 1 second is

### Part B

In one complete revolution, the electrons will go back to its original position. Thus, there is no net displacement. Therefore,