Applications of Coulomb’s Law

Physics 12

Coulomb Sample Problem

Three charges are arranged in a line; if the three charges are 15μC, -12μC and 18μC respectively. The distance between the first two charges is 0.20m and the second and third charges is 0.30m. What is the force experienced by the first charge?

Coulomb Sample Problem

What force is experienced by the remaining two charges?

Force (Vector) Addition

To add forces, resolve each force into its components and treat the forces in the x-direction and y-direction independently

Once you sum the x and y components, use Pythagorean Theorem and Trigonometry to resolve into a resultant force

Example

A point P has forces of 12.0N at 24.3°, 17.6N at 112°, 6.78N at 241° and 10.2N at 74.4°.Determine the resultant vector

25.5N, 81.4°

Coulomb’s Law and Vector Addition

When we consider an electrostatic system, we need to use Coulomb’s Law to determine the magnitude and direction of each force

Once the magnitude and direction of each force has been determined, then the vector sum can be completed

Coulomb’s Law in 2D

Three charges are arranged as follows; a -2.0μC is placed 4.0m due north of a 3.0μC charge and 3.0m due west of a 5.0μC charge. What is the force experienced by the -2.0μC charge?

Coulomb’s Law in 2D

NxF

r

qkqF

e

e

312

221

12

104.3

-2.0μC

3.0 μ C

5.0 μ C

4.0m

3.0m

NxF

r

qkqF

e

e

323

223

23

104.5

1

2

3

Coulomb’s Law in 2D

o

oo

233

18053

3.0 μ C2

NxF

NxF

NxF

NxF

NxF

NF

ye

ye

xe

xe

ye

xe

323

323

323

323

312

12

103.4

233sin104.5

102.3

233cos104.5

104.3

0

Coulomb’s Law in 2D

Use the x and y component data to determine the resultant force vector

NxF

NxNxF

NxF

NxNF

ey

ey

ex

ex

4

33

3

3

100.9

103.4104.3

102.3

102.30

oe

o

e

NxF

NxF

196,103.3

16

103.3

3

3

Practice Problems

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