Everything Science Grade 11

17.2 CHAPTER 17. ELECTROSTATICS

Thus the magnitude of the force is 3 , 37 × 10 −^8 N. However since both

point charges have opposite signs, the force willbe attractive.

Next is another examplethat demonstrates the difference in magnitude between the gravitational
force and the electrostatic force.

Example 2: Coulomb’s Law II

QUESTION

Determine the electrostatic force and gravitational force between two electrons 10 −^10 m apart

(i.e. the forces felt insidean atom).

SOLUTION

Step 1 : Determine what is required

We are required to calculate the electrostatic andgravitational forces between

two electrons, a given distance apart.

Step 2 : Determine how to approach the problem

We can use:

Fe= k

Q 1 Q 2

r^2

to calculate the electrostatic force and

Fg= G

m 1 m 2

r^2

to calculate the gravitational force.

Step 3 : Determine what is given

• Q 1 = Q 2 = 1, 6 × 10 −^19 C(The charge on an electron)


• m 1 = m 2 = 9, 1 × 10 −^31 kg(The mass of an electron)


• r = 1× 10 −^10 m
  We know that:


• k = 8, 99 × 109 N· m^2 · C−^2


• G = 6, 67 × 10 −^11 N· m^2 · kg−^2
  All quantities are in SI units.
  We can draw a diagramof the situation.

Q 1 =− 1 , 60 × 10 −^19 C Q 2 =− 1 , 60 × 10 −^19 C

� �

10 −^10 m

Step 4 : Calculate the electrostatic force