1. Electric Force & Coulomb’s Law
Charles Augustin de Coulomb
Inverse Square Rule
What is a Coulomb?
FE vs. Fg
Calculating the Net Electric Force on an object

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4. The Electric Force _________
A very important and strong fundamental force
Includes the interaction of negative electrons and the positive nuclei they orbit

5. Charles Augustin de Coulomb
Developed the force relationship between electric charges in the 1780’s (now known as Coulomb’s Law).
Showed that the electric force between two objects follows the inverse square law

6. Inverse square law Review
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Force (N)
Separation (m)

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8. What is a Coulomb?
A coulomb is approximately the amount of electric charge that passes through a standard 60-W light bulb in 2 s.
______
An electrostatic shock that you might receive from touching a metallic doorknob would be much less than a microcoulomb (10-6 C).
A lightning bolt may transfer up to 20 C

9. Check Your Understanding
The magnitude of the electrostatic force between two small, essentially point-like, charged objects is 5.0 x 10-5 N. Calculate the force for each of the following situations:
The distance between the charges is doubled, while the size of the charges stays the same.
The charge on one object is tripled, while the charge on the other is halved.
k = (9.0 x 109 Nm2/C2)

10. Check Your Understanding
What is the magnitude of the force of repulsion between two small spheres 1.0 m apart, if each has a charge of 1.0 x C?
k = (9.0 x 109 Nm2/C2)

11. Electric Force (FE) vs. Gravitational Force (Fg)
Similarities:
Both are inverse square laws that are also proportional to the product of another quantity
for gravity it is the product of two masses, and for the electric force it is the product of the two charges.
Distance in both cases is measured from the centres of the spheres

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13. Newton’s 3rd Law
Newton’s Third Law – For every action there is an equal and opposite reaction. The electric force exerted on body A by body B is equal in magnitude and opposite in direction to the force exerted on B by A.

14. Calculating the Net Electric Force on an object
The net force on a single charge is the vector sum of all independently calculated forces acting on it.
Only compare two objects at a time
Just like before
Find the x and y components
Setup your triangle
Solve for the hypotenuse
Include the direction

15. Check Your Understanding
Charged spheres A and B are fixed in position (see the diagram below) and have charges x 10-6 C and -2.5 x 10-7 C, respectively. Calculate the net force on sphere C, whose charge is +6.4 x 10-6 C.
k = (9.0 x 109 Nm2/C2)

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