1. Electric Fields and Forces

2. Electrostatics
“Electricity at rest”

3. Electric Charges Fundamental positive charge – proton
Fundamental negative charge – electron
If an object gains electrons – becomes negative
If an object loses electrons – becomes positive

4. Measuring the Charge Unit of charge is coulomb (C)
Elementary charge (e) of electron and proton – 1.6x C.
1 C – 6.24x1018 electrons
Braun Electroscope – device for detecting electric charge

5. Conservation of Charge
Charge cannot be created or destroyed, only transferred from one object to another.

6. Transferring of Charges
(Electroscopes, Metal Spheres)

7. Coulomb’s Law Force two charges have on each other
Related to Newton’s Law of Universal Gravitation
q1 and q2 are charges
r – distance between centers
k – electrostatic constant (9.0x109 Nm2 /C2)
Fe = magnitude of force (N)

8. Force vs. Distance
Force
Distance

9. Example
Calculate the magnitude of the force between two positive charges, q1 = 3.0 x10-6 and q2 = 6.0 x10-5 C, separated by a distance of 9.0 m.
(Positive value of F – Repulsion)
(Negative value of F – Attraction)

10. Electric Field
A field exists when an electric force is exerted on a charged particle
Vector Quantity
Idea developed by Michael Faraday
Electric Field Lines – Models to represent an electric field
Lines ALWAYS go AWAY from positive charges

11. Electric Field Lines

12. Electric Field Lines Two Equal and Opposite Charges
Two like charges (+ and -)
Parallel Plates
Hollow Sphere
Directionality of a point charge.

13. Electric Field Strength
F – Force (N)
E – Electric Field Strength (N/C)
q – charge (C)

14. Example
A test charge of +2.0x10-6 coulomb experiences a force of 2.4x10-3 N when placed in an electric field. Determine the magnitude of the field.

15. Potential Difference
The work required to bring a charge from infinity to that point.
When work is done, energy is used
Scalar Quantity

16. Potential Difference V – Potential Difference (Volts, V)
W – Work (Joules, J)
q – charge (Coulombs, C)

17. Problem
When a charge of -4x10-3 C is moved between 2 points in an electric field, 0.8 J of work is done on the charge. Calculate the potential difference between the points

18. Electron Volt
Electron Volt (eV) is the energy required to move one elementary charge (1.6x C)
1 eV = 1.6x C