Coulomb’s Law
1.3 Coulomb’s Law
Learning Objectives
By the end of this section, you will be able to:
- Describe the electric force, both qualitatively and quantitatively
- Calculate the force that charges exert on each other
- Determine the direction of the electric force for different source charges
- Correctly describe and apply the superposition principle for multiple source charges
Coulomb’s Law
The magnitude of the electric force (or Coulomb force) between two electrically charged particles is equal to
If the charges have the same sign, the force is in the same direction as r showing a repelling force. If the charges have different signs, the force is in the opposite direction of r showing an attracting force.
Discuss!
Reflect on this question and take notes on how you would answer it. Then we will share these thoughts together in a class discussion.
Compare the magnitudes of the gravitational and electric forces exerted by the nucleus of a hydrogen atom on an electron when the two are 0.050 nm apart.
| Pause & Predict 1.3.1 |
|---|
| What is the force exerted on the proton from the electron? |
A. 7.91 x 10-16 N (- ) |
| B. 4.27 x 10-22 N (-) |
| C. 9.88 x 103 N (-) |
| D. 7.91 x 10-20 N |
| E. 4.27 x 10-24 N |
| Pause & Predict 1.3.2 |
|---|
| What is the force on the proton due to these other charges? |
| A. 1.78 x 10-15 N |
| B. 3.56 x 10-15 N |
| C. 3.98 x 10-15 N |
| D. 5.34 x 10-15 N |
| E. 7.30 x 10-8 N |
Practice!
| Practice 1.3.1 |
|---|
| A proton and an electron are fixed 1.75 nm apart from each other. What is the force exerted on the electron due to the proton? |
| A. 9.41 × 108 N, towards the proton |
| B. 9.41 × 108 N, away from the proton |
| C. 1.32 × 10-19 N, towards the proton |
| D. 1.32 × 10-19 N, away from the proton |
| E. 7.53 × 10-11 N, towards the proton |
| F. 7.53 × 10-11 N, away from the proton |
| Practice 1.3.2 |
|---|
 Two protons and an electron are fixed on the corners of a rectangle, as shown. One proton is at (0 nm, 1.75 nm) and the other proton is at (1.15 nm, 0 nm). The electron is fixed at (1.15 nm, 1.75 nm). What is the magnitude of the force on the electron due to the two protons? |
| A. 1.74 × 10-10 N |
| B. 7.53 × 10-11 N |
| C. 1.90 × 10-10 N |
| D. 2.50 × 10-10 N |
| Practice 1.3.3 |
|---|
Two protons and an electron are fixed on the corners of a rectangle, as shown. One proton is at (0 nm, 1.75 nm) and the other proton is at (1.15 nm, 0 nm). The electron is fixed at (1.15 nm, 1.75 nm). What is the angle made by the force on the electron due to the two protons, measured with respect to the +x axis? |
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