# Two protons in a molecule are 4.00*10^-10 m apart. Find the electric force exerted by one proton on the other.

(a) Two protons in a molecule are 4.00 10-10 m apart. Find the electric force exerted by one proton on the other.

 magnitude N direction

(b) State how the magnitude of this force compares with the magnitude of the gravitational force exerted by one proton on the other.

 Fe Fg

=

(c) What must be a particle's charge-to-mass ratio if the magnitude of the gravitational force between two of these particles is equal to the magnitude of electric force between them?
C/kg

asked Jan 15, 2012 in Physics
edited Feb 5, 2012

+1 vote

Part A: to find the electric force exerted use Colulomb's Law, which gives the following formula:

$F = k_\mathrm{e} \frac{q_1q_2}{r^2}$
ke=8.98*10^9 N*m^2/C^2

q1 and q2 are the charge of the proton, which is 1.602*10^-19 C

and r is the distance between the two particles which is given in the equation: 4.00 10-10 m

Now plug these values into the equation and solve to get:
1.44*10^-9 N

Now for Part B you are comparing the ratio of the electric force to the gravitational force, which is given by the formula below:

where G is your gravitational constant which equals: 6.674*10^-11 N*m^2/kg^2

and m1 and m2 are the mass of the particles which are each: 1.673*10^-27kg

and r is once again 4.00 10-10 m.

The gravitational force is found to be: 1.1675*10^-45 N

Now the ratio would just be your answer from Part A divided by 1.1675*10^-45 N, which would result in 1.23*10^36 as the answer.

Lastly, for Part C you are finding the ratio of the charge to the mass, or q/m.

To do this set the equations for the gravitational force equal to the equation for the electric force as follows:

Fg=Fe

(G*m1m2)/r^2 = (ke*q1q2)/r^2

now move the variables around until you have a ratio of q/m,
hence:

(q/m)=(G/ke)^(1/2)

q/m = 8.61753*10^-11
answered Jan 17, 2012 by ~Expert~ (3,020 points)
selected Jan 20, 2012 by Roar3215