Centripetal Forces

Question

Let’s compare this electrical force to the force of gravity. Imagine you could place 1 g of electrons 1.0 m away from another 1 g of electrons. Calculate:
a) the electrical force of repulsion between the two charge collections.
b) the gravitational force of attraction between them.
c) the ratio of the electrical force to the gravitational force.
d) Discuss whether you think gravity would play a major part in holding atoms together. Refer to your results above.

 

Will someone please help me with this question! 

Answer 1

I will set this up for you and you can crunch out the numbers.

 

(a)

 

Look up the charge e and mass m_e of an electron in tables.  

 

Compute N = number of electrons = 1 g divided by the mass of a single electron

 

Then the electric force is

 

F_e = k(Ne)²/r²

 

Find k in tables.  You are given r.

 

(b)

 

F_g = G(Nm_e)²/r²

 

Find G in tables.

 

(c)

 

F_e/F_g = [k(Ne)²/r²] / [G(Nm_e)²/r²] = (k/G) (e/m_e)²

 

(d)

 

When you crunch out the numbers, you will find that the electrical force is vastly larger than the gravitational force, so the gravitational force is negligible in atomic physics.