1. Electricity & Magnetism

2. Electrostatics Ch 32

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

4. Static Electricty
Electric charges that are at rest

5. 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

6. Subatomic Particles Particle Proton Neutron Electron Location
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
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)
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)
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)
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 ?
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?

13. 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!!!!

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

15. 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

16. 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

17. 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.

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

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

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

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

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

25. 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

26. Charging by Friction
Objects become charged when they are rubbed together
One becomes (+) while the other becomes (–)
Gaining electrons becomes negative
Losing electrons becomes positive
Both will have equal charge, opposite sign

27. Electroscope
Object used to detect and measure electric charge on an object + - - + + -

28. Electroscope – Charge separation + + - - - - + +

29. Charging by Conduction
When 2 conductors of unequal charges touch, the electrons will move to balance out the charge, leaving both conductors with the same (equal) charge -6
-10 +4 -3

30. Charging by conduction using - rod
e- rod to
scope -
Scope charged
negative + -
e- scope to
ground + -

31. Charging by conduction using + rod
e- scope to
rod +
Scope charged
positive + -
e- ground
to scope + -

32. Charging by Induction
If a charged object is brought near a conducting surface, even without physical contact, electrons will move in the conducting surface.
Read 32.6

33. Charging by Induction

34. Charging by induction using - rod+ -
e- scope to
ground + - +
Scope charged
positive + + -

35. Charging by induction using + rod- - +
e- ground
to scope + -
Scope charged
negative - + -

37. Electric Fields Ch 33

38. 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

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

40. Electric Field Lines

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

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

44. Electric Field Strength

45. 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? + -

46. 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

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

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

49. 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

50. Why something moves
Gravitational
Electrical

52. Electric Current
Chapter 34

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

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

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

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

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

58. 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

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

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

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

62. Ohm’s Law

64. Circuit Continuous loop that allows for the flow of charges
Must follow Ohm’s Law
Overall and individual components

65. Electric Power
Rate at which electrical energy is converted into another form such as mechanical, heat, and light.
Measured in Watts(W)

66. Power

67. Electrical Power
P (W)
I (A)
V (V)
1 W = 1 A*V

68. Electrical Power

70. Electrical Energy (Work)
W (J)
P (W)
t (s)

71. Electrical Energy (Work)

72. Kilowatt-Hour (kW-hr)
Amount of energy consumed in 1 hour at a rate of 1 kilowatt

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

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

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

77. Length
More Length increases Resistance L R

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

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

80. 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

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

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

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

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

85. Temperature Increasing Temperature increases Resistivity
Increasing Temperature increases Resistance

86. Resistors

87. Resistor Color Code 4 bands First band is first number
Second band is second number
Third band is multiplier (x10, …)
Last band indicates tolerance (±%)

90. Circuits
Chapter 35

91. Simple Circuit
Continuous loop for electrons to move (current)

92. Simple Circuit Simple Circuit includes: Power source (battery)
Connecting wires (no resistance)
Electrical device (resistors, lights, etc)
Switch (optional)

93. Circuit Symbols
Power source
Connecting Wires
Resistor
Switch

94. Basic Circuit

95. Ohm’s Law
Reminder: Circuits as a whole and individual resistors must obey Ohm’s Law
V = IR

96. Measuring Current Ammeter Measures current as it flows through meter
Must be connected IN the flow
Very low resistance in meter

97. Circuit with Ammeter A

98. Measuring Potential Difference
Voltmeter
Measures the difference between two points
Must be connected to TWO points
Outside loop
Very high resistance in voltmeter
No current flows through voltmeter

99. Circuit with Voltmeter

100. Series Circuits
Multiple electrical devices, resistors, in one continuous loop

101. Series Circuits Current must flow equally through all resistors.
IT = I1 = I2 = …

102. Series Circuits
For a complete loop, potential gains must equal potential drops.(Kirchhoff’s Loop Rule)
VT = V1 + V2 + V3 + …

103. Equivalent Resistance
Equivalent resistance is the idea that all the resistors in a circuit can be removed and a single resistor can be placed in the circuit and have the same resistance as if the original resistors were still in place.

104. Series Circuits VT = V1 + V2 + V3 + V4 IRT = IR1 + IR2 + IR3 + IR4
IRT = I(R1 + R2 + R3 + R4)
RT = R1 + R2 + R3 + R4

105. Series Circuits
For series circuits, the equivalent resistance is equal to the sum of each resistor
RS = R1 + R2 + R3 + R4 + …

107. Parallel Circuits
Multiple electrical devices, or resistors, in multiple loops.

108. Parallel Circuits
Potential Difference, voltage, across each resistor is the same (Kirchhoff’s Loop Rule)
VT = V1 = V2 = …

109. Parallel Circuits
Total Current entering junction must equal total current leaving junction (Kirchhoff’s Junction Rule)
IT = I1 + I2 + I3 + … IT I1 I2

110. Parallel Circuits
Equivalent Resistance for Parallel Circuits follows the following equation:

112. Combination Circuits
Circuits that have both series and parallel parts.

113. Combination Circuits
Combination circuits must follow Ohm’s Law
V = IR

114. Combination Circuits
Use idea of equivalent resistance to simplify circuit

115. Combination Circuits
120V
30Ω
15Ω
15Ω
Req = ?
30Ω

116. Combination Circuits
120V
30Ω
15Ω
15Ω
30Ω

117. Combination Circuits
30Ω
120V

118. Combination Circuits
10Ω
120V
Req =10Ω

119. Combination Circuits 4Ω
30Ω
120V
10Ω
15Ω
20Ω
40Ω
20Ω
Req = ?

120. Combination Circuits 4Ω
30Ω
120V
10Ω
15Ω
60Ω
20Ω

121. Combination Circuits
15Ω
120V 4Ω
15Ω
10Ω
30Ω

122. Combination Circuits
120V 4Ω
15Ω 5Ω

123. Combination Circuits
24Ω
120V
Req = 24Ω

125. Magnetism
Chapter 36

126. What is a Magnet? Material or object that produces a magnetic field.
Two types:
Permanent
Electromagnet

127. What causes Magnetism?
In order to create a magnetic field, a charged particle must be moving.
Moving and spinning electrons cause magnetic fields in every object.

128. Domains
A small region of space where the magnetic fields produced by moving electrons are aligned together.
Often, the directions of the domains cancel each other out.
Ferromagnetic material
Cancellations do not occur, resulting in a net magnetic field

129. Domains

130. Magnetism Opposites poles attract Like poles Repel
Magnetic Poles can not be separated
Every object that has a north pole has a south pole

131. Magnetism

132. Magnetic Field
Region around a moving charged particle through which a force is exerted on another moving charged particle
Similar to Electric Fields

133. Magnetic Field Lines Lines are not real North  South (outside magnet)
Can not cross
Closer lines mean stronger field

134. Magnetic Field Lines

135. Magnetic Field Lines

137. Magnetic Field
Magnetic Field is a region around a moving charged object through which a force is exerted on another moving charged particle
Motion of particle must be perpendicular to the magnetic field

138. Magnetic Fields
Magnetic Fields are often illustrated using arrows

139. Magnetic Fields What about into the page or out of the page? Into Page
Out of Page

140. Magnetic Hand Rules
To determine the direction of the force, we use hand rules.
Different hands for different charges
Right hand for Positive charges
Left hand for Negative charges

141. Conventional Current
Conventional Current follows the old “convention” that positive charges are the charges that are moving in current
Use Right Hand Rule

142. Electron Current
Electron Current is the reality that negative charges are the charges that are moving in current
Use Left Hand Rule

143. Magnetic Hand Rules Point index finger in direction of motion
Point palm or other fingers in direction of magnetic field
Point thumb in direction of Magnetic Force

144. Example
An electron is moving through a magnetic field as shown below. In what direction will the magnetic force be?
Out of page e

145. Another Example
An electron is moving through a magnetic field as shown below. In what direction will the magnetic force be?
Down e

146. Force on Wire
Still use hand rule to determine the direction of the magnetic force
Index finger is the direction of the current

147. Magnetic Fields produced by Currents
A current carrying wire also produces a magnetic field
Direction follows second Hand Rule

148. Magnetic Fields produced by Currents
Second Hand Rule
Thumb in direction of current
Curl fingers around wire
Curled fingers show direction of magnetic field

149. Example
What is the direction of the magnetic force exerted on wire 2 by the magnetic field produced by wire 1? I- 1 2 I-
Down

150. Example
What is the direction of the magnetic force exerted on wire 1 by the magnetic field produced by wire 2? I- 1 2 I-
Down

151. Magnetic Fields produced by current carrying loops
Imagine current flowing through the loop below
In what direction will the magnetic field be produced inside the loop?
Into Page I-

153. Electromagnets
Temporary magnet caused by an induced magnetic field from current carrying wires.

154. Electromagnets Current carrying wire produces a magnetic field
Coiling the wire bunches up the magnetic field inside the coil

155. Electromagnets Increasing the strength of the electromagnet:
Increase Current in wire
Increase number of coils
Add an iron core

157. Electromagnetic Induction
If charged particle moving through a magnetic field feels a force, shouldn’t a moving magnetic field exert a force on a charged particle?

158. Electromagnetic Induction
A voltage can be “induced” in a wire by moving a magnet near the wire.
often a coil of wire is used
Faraday’s Law
Induced voltage is directly proportional to the number of coils, cross-sectional area of the coils, and rate of change of magnetic field

159. Electromagnetic Induction

160. Electromagnetic Induction

161. Electromagnetic Induction
Inducing a current in a coil of wire creates its own magnetic field

162. Electromagnetic Induction
Changing direction of magnetic field changes direction of induced voltage
Creating an alternating current (AC)

163. Alternating Current Direct Current
Current alternates direction at a regular rate
Electrical Outlets
Direct Current
Current flows in one direction only
Batteries
Sim

164. Generators & Motors
Device to convert between Electrical and Mechanical Energy
Generator
Converts Mechanical Energy to Electrical Energy
Motor
Converts Electrical energy to Mechanical Energy

165. Generator

166. Motor

168. Electromagnetic Induction
Current flowing through a coil wires produces a magnetic field
A changing magnetic field induces a current in an adjacent coil

169. Electromagnetic Induction
Using AC produces a consistent changing magnetic field
Adding an iron core strengthens the magnetic field

170. Transformer
Device used to increase or decrease voltage using electromagnetic induction

171. Transformer
Complete loop is more efficient

172. Transformers
V = voltage
N = number of coils

173. Transformers Step Up Transformer Step Down Transformer
Secondary has more coils than primary
Resulting Voltage is larger
Step Down Transformer
Secondary has less coils than primary
Resulting voltage is lower

174. Conservation of Energy
Energy transferred must be equal
Power is equal

176. Electric Field An electric field is produced by a charged particle
A changing electric field can be produced by a moving charged particle
A changing electric field produces a magnetic field

177. Electromagnetic Induction
A changing magnetic field also induces an electric field
When magnetic fields and electric fields are produced they are at right angles to each other

178. Electromagnetic Wave
Oscillating electric and magnetic fields that regenerate each other (light)
No medium is required

179. Electromagnetic Radiation
Only one speed can preserve this regeneration
Speed of Light is 300,000,000 m/s
3 x 108 m/s
Discovered by James Clerk Maxwell

180. Maxwell’s Equations