1. Electricity

2. Basic Concept In Mechanics, the basic property of matter is Mass.
In Electricity, the basic property is Charge.

3. Electrostatics
Static Electricity
Electric charges that are at rest

4. Basic Units Compare Smallest Possible Unit Practical Unit US Currency
Penny
$0.01 = 1/100th of a dollar
Dollar
$1 = 100 Pennies
Electric
Charge
Elementary Charge (1e)
electron or proton
1e = 1.6 x 10-19C
Coulomb
1C = 6.25 x 1018e

5. Subatomic Particles Particle Proton Neutron Electron Location
Relative Charge
Actual Charge (C)
Relative mass (u)
Actual mass (kg)
Easily detected ?
Easily removed?

6. Subatomic Particles Particle Proton Neutron Electron Location Nucleus
Outside Nucleus
Relative Charge
Actual Charge (C)
Relative mass (u)
Actual mass (kg)
Easily detected ?
Easily removed?

7. Subatomic Particles Particle Proton Neutron Electron Location Nucleus
Outside Nucleus
Relative Charge +1 -1
Actual Charge (C)
Relative mass (u)
Actual mass (kg)
Easily detected ?
Easily removed?

8. Subatomic Particles Particle Proton Neutron Electron Location Nucleus
Outside Nucleus
Relative Charge +1 -1
Actual Charge (C)
+1.6 x 10-19
-1.6 x 10-19
Relative mass (u)
Actual mass (kg)
Easily detected ?
Easily removed?

9. Subatomic Particles Particle Proton Neutron Electron Location Nucleus
Outside Nucleus
Relative Charge +1 -1
Actual Charge (C)
+1.6 x 10-19
-1.6 x 10-19
Relative mass (u) 1
Actual mass (kg)
Easily detected ?
Easily removed?

10. Subatomic Particles Particle Proton Neutron Electron Location Nucleus
Outside Nucleus
Relative Charge +1 -1
Actual Charge (C)
+1.6 x 10-19
-1.6 x 10-19
Relative mass (u) 1
Actual mass (kg)
1.67 x 10-27
9.11 x 10-31
Easily detected ?
Easily removed?

11. Subatomic Particles Particle Proton Neutron Electron Location Nucleus
Outside Nucleus
Relative Charge +1 -1
Actual Charge (C)
+1.6 x 10-19
-1.6 x 10-19
Relative mass (u) 1
Actual mass (kg)
1.67 x 10-27
9.11 x 10-31
Easily detected ?
yes no
Yes
Easily removed?

12. Subatomic Particles Particle Proton Neutron Electron Location Nucleus
Outside Nucleus
Relative Charge +1 -1
Actual Charge (C)
+1.6 x 10-19
-1.6 x 10-19
Relative mass (u) 1
Actual mass (kg)
1.67 x 10-27
9.11 x 10-31
Easily detected ?
yes no
Yes
Easily removed?
NO!!!!

13. Charged objects
Positively charged objects have less electrons than protons
Negatively charged objects have more electrons than protons
Neutral objects have equal amounts of protons and electrons

14. Law of Charges Opposite charges attract Like charges repel
Neutral objects are attracted to positive or negative objects because of polarization
Polarization
Separation of charges without charging object

15. Examples
How many electrons are on a conductor if it has a charge of -4 x C?
250 electrons
What charge will 120 protons have?
+1.92 x C

16. Example
Why is it not possible for any object to have a charge of -8 x C?
Electrons (or protons) cannot be broken down into smaller pieces.

17. Movement of Charge Conductors Insulators Electrons are free to move
Most metals
Insulators
Electrons are not free to move

18. Movement of Charge Grounding Examples
Excess charges on an object will try to move away from like charges or towards opposite charges
Examples
Lightning, Static electricity

20. Review Gravitational Force What factors affect gravitational force?
Size of each mass
Distance of separation

21. Electrostatic Force
What factors will affect the amount of attraction or repulsion?
Size of each charge
Distance of separation

22. Coulomb’s Law k = Electrostatic constant, 8.99 x 109 Nm2/C2
q = charge (C)
r = distance separating the center of each charge (m)

23. Remember Opposite charges attract Like charges repel
-F means attractive force
+F means repulsive force

25. Electric Fields
Electric Field is a region around a charged object through which a force is exerted on any other charged particle.
Direction of the electric field is the direction a positive charge would move if placed in the field

26. Electric Field Lines Lines are not real Positive  Negative
Can not cross
Closer lines mean stronger field

27. Electric Field Lines

28. Electric Fields Parallel Plates
Electric Field is uniform between plates

29. Electric Field Strength, E
Force per charge
Amount of force felt by a charge
Vector
E (N/C)
Fe (N)
q (C)

30. Electric Field Strength

32. Work Which way will each particle be pushed by the electric field?
Which way does work have to be exerted in order to move each particle against the electric field? + -

33. Electric Potential Difference
Amount of work done per unit charge as a charged particle is moved between points
A.K.A.
Electric Potential
Potential Difference
Voltage

34. Electric Potential Difference
V (V)
W (J)
q (C)
1 V = 1 J/C

35. Electric Potential Difference
Rearranged
(1C)*(1V) = 1J

36. Electron Volts (eV)
Amount of work(energy) done by 1 volt on 1 electron
Unit of Energy
(1C)(1V)=1J
(1e)(1V)=1eV
1eV = 1.6 x 10-19J

37. Why something moves
Gravitational
Electrical

39. Electrodynamics The study of charges and their motion
Often use an analogy of water moving to illustrate

40. Flow A measure of water flow is called ____? Current
How much charge flows per unit time

41. Current
q (C)
t (s)
1 Ampere (A) = 1 C/s

42. Current Which charge flows? Negatives (Reality) Conventional Current
Positive charges (rest of the physics world)
Electrons actually move

43. Motion What causes water to move?
Change in height (Potential Difference)
Water, flows from high potential to low potential

44. Voltage Electrical Potential difference causes charges to move.
Batteries provide a Potential Difference
Batteries act like a pump to raise charges from a low to high potential

45. Resistance Opposition to flow
Any device that opposes the flow of current can be called a resistor
Unit is Ohm, Ω

46. Ohm’s Law Potential Difference encourages charges to flow
Resistance discourages charges to flow
Ratio of Potential Difference to Resistance equals Current

47. Ohm’s Law
V (V)
I (A)
R (Ω)
1 V = 1 A* Ω

48. Ohm’s Law

50. Resistance What factors affect the resistance of a material? Size
Type of material
Temperature

51. Resistance The size of a resistor affects the resistance Length
Cross-sectional Area

52. Length
Would water flow faster through a short pipe or a long pipe?

53. Length
More Length increases Resistance L R

54. Cross-Sectional Area
Would more water flow through a wide pipe or narrow pipe?

55. Cross-Sectional Area
Larger Area decreases Resistance A R

56. Type of Material How does the type of material affect resistance?
Electrons need to flow through the resistor.
The more material that gets in the way, the slower the electrons

57. Resistivity, ρ Measure of how resistive a material is.
As Resistivity increases Resistance Increases ρ R

58. All together now R (Ω) L (m) A (m2) ρ (Ω *m)
Selected materials in reference tables

59. Temperature How would temperature affect resistivity?
What does increasing the temperature do to the molecules in a resistor?
Increasing Temp increases molecular movement

60. Temperature
Imagine walking down the hall with sophomores standing every where.
Imagine walking down the hall with sophomores running every where.
Which is easier?

61. Temperature Increasing Temperature increases Resistivity
Increasing Temperature increases Resistance