1. Coulomb’s Law Problems

2. Gravity vs. electric force
The electron and proton of a hydrogen atom are separated, on average, by a distance of about 5.3x10-11m. Find the magnitudes of the electric force and the gravitational force that each particle exerts on the other. me = 9.109x10-31kg mp = 1.673x10-27kg e = 1.60x10-19C k = 8.99x109Nm2/C2 ANSWER: Fe = 8.2x10-8N, Fg = 3.6x10-47N

3. Large electric force
Calculate the force between a +1C and -1C object if they are placed 1.0km away from each other. ANSWER: 9000N

4. Hydrogen atom – Bohr model
Calculate the speed of an electron in a circular orbit around a proton if the radius of the atom is 5.29x10-11m me = 9.109x10-31kg mp = 1.673x10-27kg e = 1.60x10-19C k = 8.99x109Nm2/C2 ANSWER: 2.18x106m/s

5. Principle of Superposition
If there are multiple point charges, the resultant force on one particle is the vector sum of the individual forces on that charge.
Principle of Superposition

6. Three charges on a line Find the force on particle 1. ANSWER: +5.7N 23
0.2m
0.15m
-4.0μC
+3.0 μC
-7.0 μC

7. Three charges in a plane2
Find the force on particle 1. ANSWER: 24o
-6.0 μC
0.15m
73o 1 3
0.1m
+4.0 μC
-5.0 μC

8. Two 1. 1g balloons are suspended from 2
Two 1.1g balloons are suspended from 2.0m long strings and hung from the ceiling. They are then rubbed 10 times with animal fur to impart an identical charge Q to each balloon. The balloons repel each other and each string is observed to make an angle of 15° with the vertical. Determine the electric force of repulsion, the charge on each balloon, and the quantity of electrons transferred to each balloon as a result of 10 rubs with animal fur.