Vincent Selhorst-Jones

Light

Slide Duration:

Section 1: Motion
Math Review

16m 49s

Intro
0:00
The Metric System
0:26
Distance, Mass, Volume, and Time
0:27
Scientific Notation
1:40
Examples: 47,000,000,000 and 0.00000002
1:41
Significant Figures
3:18
Significant Figures Overview
3:19
Properties of Significant Figures
4:04
How Significant Figures Interact
7:00
Trigonometry Review
8:57
Pythagorean Theorem, sine, cosine, and tangent
8:58
Inverse Trigonometric Functions
9:48
Inverse Trigonometric Functions
9:49
Vectors
10:44
Vectors
10:45
Scalars
12:10
Scalars
12:11
Breaking a Vector into Components
13:17
Breaking a Vector into Components
13:18
Length of a Vector
13:58
Length of a Vector
13:59
Relationship Between Length, Angle, and Coordinates
14:45
One Dimensional Kinematics

26m 2s

Intro
0:00
Position
0:06
Definition and Example of Position
0:07
Distance
1:11
Definition and Example of Distance
1:12
Displacement
1:34
Definition and Example of Displacement
1:35
Comparison
2:45
Distance vs. Displacement
2:46
Notation
2:54
Notation for Location, Distance, and Displacement
2:55
Speed
3:32
Definition and Formula for Speed
3:33
Example: Speed
3:51
Velocity
4:23
Definition and Formula for Velocity
4:24
∆ - Greek: 'Delta'
5:01
∆ or 'Change In'
5:02
Acceleration
6:02
Definition and Formula for Acceleration
6:03
Example: Acceleration
6:38
Gravity
7:31
Gravity
7:32
Formulas
8:44
Kinematics Formula 1
8:45
Kinematics Formula 2
9:32
Definitional Formulas
14:00
Example 1: Speed of a Rock Being Thrown
14:12
Example 2: How Long Does It Take for the Rock to Hit the Ground?
15:37
Example 3: Acceleration of a Biker
21:09
Example 4: Velocity and Displacement of a UFO
22:43
Multi-Dimensional Kinematics

29m 59s

Intro
0:00
0:07
Scalars and Vectors
0:08
A Note on Vectors
2:12
Indicating Vectors
2:13
Position
3:03
Position
3:04
Distance and Displacement
3:35
Distance and Displacement: Definitions
3:36
Distance and Displacement: Example
4:39
Speed and Velocity
8:57
Speed and Velocity: Definition & Formulas
8:58
Speed and Velocity: Example
10:06
Speed from Velocity
12:01
Speed from Velocity
12:02
Acceleration
14:09
Acceleration
14:10
Gravity
14:26
Gravity
14:27
Formulas
15:11
Formulas with Vectors
15:12
Example 1: Average Acceleration
16:57
Example 2A: Initial Velocity
19:14
Example 2B: How Long Does It Take for the Ball to Hit the Ground?
21:35
Example 2C: Displacement
26:46
Frames of Reference

18m 36s

Intro
0:00
Fundamental Example
0:25
Fundamental Example Part 1
0:26
Fundamental Example Part 2
1:20
General Case
2:36
Particle P and Two Observers A and B
2:37
Speed of P from A's Frame of Reference
3:05
3:22
Acceleration Shows the Change in Velocity
3:23
Acceleration when Velocity is Constant
3:48
Multi-Dimensional Case
4:35
Multi-Dimensional Case
4:36
Some Notes
5:04
Choosing the Frame of Reference
5:05
Example 1: What Velocity does the Ball have from the Frame of Reference of a Stationary Observer?
7:27
Example 2: Velocity, Speed, and Displacement
9:26
Example 3: Speed and Acceleration in the Reference Frame
12:44
Uniform Circular Motion

16m 34s

Intro
0:00
Centripetal Acceleration
1:21
Centripetal Acceleration of a Rock Being Twirled Around on a String
1:22
Looking Closer: Instantaneous Velocity and Tangential Velocity
2:35
Magnitude of Acceleration
3:55
Centripetal Acceleration Formula
5:14
You Say You Want a Revolution
6:11
What is a Revolution?
6:12
How Long Does it Take to Complete One Revolution Around the Circle?
6:51
Example 1: Centripetal Acceleration of a Rock
7:40
Example 2: Magnitude of a Car's Acceleration While Turning
9:20
Example 3: Speed of a Point on the Edge of a US Quarter
13:10
Section 2: Force
Newton's 1st Law

12m 37s

Intro
0:00
Newton's First Law/ Law of Inertia
2:45
A Body's Velocity Remains Constant Unless Acted Upon by a Force
2:46
Mass & Inertia
4:07
Mass & Inertia
4:08
Mass & Volume
5:49
Mass & Volume
5:50
Mass & Weight
7:08
Mass & Weight
7:09
Example 1: The Speed of a Rocket
8:47
Example 2: Which of the Following Has More Inertia?
10:06
Example 3: Change in Inertia
11:51
Newton's 2nd Law: Introduction

27m 5s

Intro
0:00
Net Force
1:42
Consider a Block That is Pushed On Equally From Both Sides
1:43
What if One of the Forces was Greater Than the Other?
2:29
The Net Force is All the Forces Put Together
2:43
Newton's Second Law
3:14
Net Force = (Mass) x (Acceleration)
3:15
Units
3:48
The Units of Newton's Second Law
3:49
Free-Body Diagram
5:34
Free-Body Diagram
5:35
Special Forces: Gravity (Weight)
8:05
Force of Gravity
8:06
Special Forces: Normal Force
9:22
Normal Force
9:23
Special Forces: Tension
10:34
Tension
10:35
Example 1: Force and Acceleration
12:19
Example 2: A 5kg Block is Pushed by Five Forces
13:24
Example 3: A 10kg Block Resting On a Table is Tethered Over a Pulley to a Free-Hanging 2kg Block
16:30
Newton's 2nd Law: Multiple Dimensions

27m 47s

Intro
0:00
Newton's 2nd Law in Multiple Dimensions
0:12
Newton's 2nd Law in Multiple Dimensions
0:13
Components
0:52
Components
0:53
Example: Force in Component Form
1:02
Special Forces
2:39
Review of Special Forces: Gravity, Normal Force, and Tension
2:40
Normal Forces
3:35
Why Do We Call It the Normal Forces?
3:36
Normal Forces on a Flat Horizontal and Vertical Surface
5:00
Normal Forces on an Incline
6:05
Example 1: A 5kg Block is Pushed By a Force of 3N to the North and a Force of 4N to the East
10:22
Example 2: A 20kg Block is On an Incline of 50° With a Rope Holding It In Place
16:08
Example 3: A 10kg Block is On an Incline of 20° Attached By Rope to a Free-hanging Block of 5kg
20:50

42m 5s

Intro
0:00
Block and Tackle Pulley System
0:30
A Single Pulley Lifting System
0:31
A Double Pulley Lifting System
1:32
2:59
Example 1: A Free-hanging, Massless String is Holding Up Three Objects of Unknown Mass
4:40
Example 2: An Object is Acted Upon by Three Forces
10:23
Example 3: A Chandelier is Suspended by a Cable From the Roof of an Elevator
17:13
Example 4: A 20kg Baboon Climbs a Massless Rope That is Attached to a 22kg Crate
23:46
Example 5: Two Blocks are Roped Together on Inclines of Different Angles
33:17
Newton's Third Law

16m 47s

Intro
0:00
Newton's Third Law
0:50
Newton's Third Law
0:51
Everyday Examples
1:24
Hammer Hitting a Nail
1:25
Swimming
2:08
Car Driving
2:35
Walking
3:15
Note
3:57
Newton's Third Law Sometimes Doesn't Come Into Play When Solving Problems: Reason 1
3:58
Newton's Third Law Sometimes Doesn't Come Into Play When Solving Problems: Reason 2
5:36
Example 1: What Force Does the Moon Pull on Earth?
7:04
Example 2: An Astronaut in Deep Space Throwing a Wrench
8:38
Example 3: A Woman Sitting in a Bosun's Chair that is Hanging from a Rope that Runs Over a Frictionless Pulley
12:51
Friction

50m 11s

Intro
0:00
Introduction
0:04
Our Intuition - Materials
0:30
Our Intuition - Weight
2:48
Our Intuition - Normal Force
3:45
The Normal Force and Friction
4:11
Two Scenarios: Same Object, Same Surface, Different Orientations
4:12
6:36
Friction as an Equation
7:23
Summing Up Friction
7:24
Friction as an Equation
7:36
The Direction of Friction
10:33
The Direction of Friction
10:34
A Quick Example
11:16
Which Block Will Accelerate Faster?
11:17
Static vs. Kinetic
14:52
Static vs. Kinetic
14:53
Static and Kinetic Coefficient of Friction
16:31
How to Use Static Friction
17:40
How to Use Static Friction
17:41
Some Examples of μs and μk
19:51
Some Examples of μs and μk
19:52
A Remark on Wheels
22:19
A Remark on Wheels
22:20
Example 1: Calculating μs and μk
28:02
Example 2: At What Angle Does the Block Begin to Slide?
31:35
Example 3: A Block is Against a Wall, Sliding Down
36:30
Example 4: Two Blocks Sitting Atop Each Other
40:16
Force & Uniform Circular Motion

26m 45s

Intro
0:00
Centripetal Force
0:46
Equations for Centripetal Force
0:47
Centripetal Force in Action
1:26
Where Does Centripetal Force Come From?
2:39
Where Does Centripetal Force Come From?
2:40
Centrifugal Force
4:05
Centrifugal Force Part 1
4:06
Centrifugal Force Part 2
6:16
Example 1: Part A - Centripetal Force On the Car
8:12
Example 1: Part B - Maximum Speed the Car Can Take the Turn At Without Slipping
8:56
Example 2: A Bucket Full of Water is Spun Around in a Vertical Circle
15:13
Example 3: A Rock is Spun Around in a Vertical Circle
21:36
Section 3: Energy
Work

28m 34s

Intro
0:00
Equivocation
0:05
Equivocation
0:06
Introduction to Work
0:32
Scenarios: 10kg Block on a Frictionless Table
0:33
Scenario: 2 Block of Different Masses
2:52
Work
4:12
Work and Force
4:13
Paralleled vs. Perpendicular
4:46
Work: A Formal Definition
7:33
An Alternate Formula
9:00
An Alternate Formula
9:01
Units
10:40
Unit for Work: Joule (J)
10:41
Example 1: Calculating Work of Force
11:32
Example 2: Work and the Force of Gravity
12:48
Example 3: A Moving Box & Force Pushing in the Opposite Direction
15:11
Example 4: Work and Forces with Directions
18:06
Example 5: Work and the Force of Gravity
23:16
Energy: Kinetic

39m 7s

Intro
0:00
Types of Energy
0:04
Types of Energy
0:05
Conservation of Energy
1:12
Conservation of Energy
1:13
What is Energy?
4:23
Energy
4:24
What is Work?
5:01
Work
5:02
Circular Definition, Much?
5:46
Circular Definition, Much?
5:47
Derivation of Kinetic Energy (Simplified)
7:44
Simplified Picture of Work
7:45
Consider the Following Three Formulas
8:42
Kinetic Energy Formula
11:01
Kinetic Energy Formula
11:02
Units
11:54
Units for Kinetic Energy
11:55
Conservation of Energy
13:24
Energy Cannot be Made or Destroyed, Only Transferred
13:25
Friction
15:02
How Does Friction Work?
15:03
Example 1: Velocity of a Block
15:59
Example 2: Energy Released During a Collision
18:28
Example 3: Speed of a Block
22:22
Example 4: Speed and Position of a Block
26:22
Energy: Gravitational Potential

28m 10s

Intro
0:00
Why Is It Called Potential Energy?
0:21
Why Is It Called Potential Energy?
0:22
Introduction to Gravitational Potential Energy
1:20
Consider an Object Dropped from Ever-Increasing heights
1:21
Gravitational Potential Energy
2:02
Gravitational Potential Energy: Derivation
2:03
Gravitational Potential Energy: Formulas
2:52
Gravitational Potential Energy: Notes
3:48
Conservation of Energy
5:50
Conservation of Energy and Formula
5:51
Example 1: Speed of a Falling Rock
6:31
Example 2: Energy Lost to Air Drag
10:58
Example 3: Distance of a Sliding Block
15:51
Example 4: Swinging Acrobat
21:32
Energy: Elastic Potential

44m 16s

Intro
0:00
Introduction to Elastic Potential
0:12
Elastic Object
0:13
Spring Example
1:11
Hooke's Law
3:27
Hooke's Law
3:28
Example of Hooke's Law
5:14
Elastic Potential Energy Formula
8:27
Elastic Potential Energy Formula
8:28
Conservation of Energy
10:17
Conservation of Energy
10:18
You Ain't Seen Nothin' Yet
12:12
You Ain't Seen Nothin' Yet
12:13
Example 1: Spring-Launcher
13:10
Example 2: Compressed Spring
18:34
Example 3: A Block Dangling From a Massless Spring
24:33
Example 4: Finding the Spring Constant
36:13
Power & Simple Machines

28m 54s

Intro
0:00
Introduction to Power & Simple Machines
0:06
What's the Difference Between a Go-Kart, a Family Van, and a Racecar?
0:07
Consider the Idea of Climbing a Flight of Stairs
1:13
Power
2:35
P= W / t
2:36
Alternate Formulas
2:59
Alternate Formulas
3:00
Units
4:24
Units for Power: Watt, Horsepower, and Kilowatt-hour
4:25
Block and Tackle, Redux
5:29
Block and Tackle Systems
5:30
Machines in General
9:44
Levers
9:45
Ramps
10:51
Example 1: Power of Force
12:22
Example 2: Power &Lifting a Watermelon
14:21
Example 3: Work and Instantaneous Power
16:05
Example 4: Power and Acceleration of a Race car
25:56
Section 4: Momentum
Center of Mass

36m 55s

Intro
0:00
Introduction to Center of Mass
0:04
Consider a Ball Tossed in the Air
0:05
Center of Mass
1:27
Definition of Center of Mass
1:28
Example of center of Mass
2:13
Center of Mass: Derivation
4:21
Center of Mass: Formula
6:44
Center of Mass: Formula, Multiple Dimensions
8:15
Center of Mass: Symmetry
9:07
Center of Mass: Non-Homogeneous
11:00
Center of Gravity
12:09
Center of Mass vs. Center of Gravity
12:10
Newton's Second Law and the Center of Mass
14:35
Newton's Second Law and the Center of Mass
14:36
Example 1: Finding The Center of Mass
16:29
Example 2: Finding The Center of Mass
18:55
Example 3: Finding The Center of Mass
21:46
Example 4: A Boy and His Mail
28:31
Linear Momentum

22m 50s

Intro
0:00
Introduction to Linear Momentum
0:04
Linear Momentum Overview
0:05
Consider the Scenarios
0:45
Linear Momentum
1:45
Definition of Linear Momentum
1:46
Impulse
3:10
Impulse
3:11
Relationship Between Impulse & Momentum
4:27
Relationship Between Impulse & Momentum
4:28
Why is It Linear Momentum?
6:55
Why is It Linear Momentum?
6:56
Example 1: Momentum of a Skateboard
8:25
Example 2: Impulse and Final Velocity
8:57
Example 3: Change in Linear Momentum and magnitude of the Impulse
13:53
Example 4: A Ball of Putty
17:07
Collisions & Linear Momentum

40m 55s

Intro
0:00
Investigating Collisions
0:45
Momentum
0:46
Center of Mass
1:26
Derivation
1:56
Extending Idea of Momentum to a System
1:57
Impulse
5:10
Conservation of Linear Momentum
6:14
Conservation of Linear Momentum
6:15
Conservation and External Forces
7:56
Conservation and External Forces
7:57
Momentum Vs. Energy
9:52
Momentum Vs. Energy
9:53
Types of Collisions
12:33
Elastic
12:34
Inelastic
12:54
Completely Inelastic
13:24
Everyday Collisions and Atomic Collisions
13:42
Example 1: Impact of Two Cars
14:07
Example 2: Billiard Balls
16:59
Example 3: Elastic Collision
23:52
Example 4: Bullet's Velocity
33:35
Section 5: Gravity
Gravity & Orbits

34m 53s

Intro
0:00
Law of Universal Gravitation
1:39
Law of Universal Gravitation
1:40
Force of Gravity Equation
2:14
Gravitational Field
5:38
Gravitational Field Overview
5:39
Gravitational Field Equation
6:32
Orbits
9:25
Orbits
9:26
The 'Falling' Moon
12:58
The 'Falling' Moon
12:59
Example 1: Force of Gravity
17:05
Example 2: Gravitational Field on the Surface of Earth
20:35
Example 3: Orbits
23:15
Example 4: Neutron Star
28:38
Section 6: Waves
Intro to Waves

35m 35s

Intro
0:00
Pulse
1:00
Introduction to Pulse
1:01
Wave
1:59
Wave Overview
2:00
Wave Types
3:16
Mechanical Waves
3:17
Electromagnetic Waves
4:01
Matter or Quantum Mechanical Waves
4:43
Transverse Waves
5:12
Longitudinal Waves
6:24
Wave Characteristics
7:24
Amplitude and Wavelength
7:25
Wave Speed (v)
10:13
Period (T)
11:02
Frequency (f)
12:33
v = λf
14:51
Wave Equation
16:15
Wave Equation
16:16
Angular Wave Number
17:34
Angular Frequency
19:36
Example 1: CPU Frequency
24:35
Example 2: Speed of Light, Wavelength, and Frequency
26:11
Example 3: Spacing of Grooves
28:35
Example 4: Wave Diagram
31:21
Waves, Cont.

52m 57s

Intro
0:00
Superposition
0:38
Superposition
0:39
Interference
1:31
Interference
1:32
Visual Example: Two Positive Pulses
2:33
Visual Example: Wave
4:02
Phase of Cycle
6:25
Phase Shift
7:31
Phase Shift
7:32
Standing Waves
9:59
Introduction to Standing Waves
10:00
Visual Examples: Standing Waves, Node, and Antinode
11:27
Standing Waves and Wavelengths
15:37
Standing Waves and Resonant Frequency
19:18
Doppler Effect
20:36
When Emitter and Receiver are Still
20:37
When Emitter is Moving Towards You
22:31
When Emitter is Moving Away
24:12
Doppler Effect: Formula
25:58
Example 1: Superposed Waves
30:00
Example 2: Superposed and Fully Destructive Interference
35:57
Example 3: Standing Waves on a String
40:45
Example 4: Police Siren
43:26
Example Sounds: 800 Hz, 906.7 Hz, 715.8 Hz, and Slide 906.7 to 715.8 Hz
48:49
Sound

36m 24s

Intro
0:00
Speed of Sound
1:26
Speed of Sound
1:27
Pitch
2:44
High Pitch & Low Pitch
2:45
Normal Hearing
3:45
Infrasonic and Ultrasonic
4:02
Intensity
4:54
Intensity: I = P/A
4:55
Intensity of Sound as an Outwardly Radiating Sphere
6:32
Decibels
9:09
Human Threshold for Hearing
9:10
Decibel (dB)
10:28
Sound Level β
11:53
Loudness Examples
13:44
Loudness Examples
13:45
Beats
15:41
Beats & Frequency
15:42
Audio Examples of Beats
17:04
Sonic Boom
20:21
Sonic Boom
20:22
Example 1: Firework
23:14
Example 2: Intensity and Decibels
24:48
Example 3: Decibels
28:24
Example 4: Frequency of a Violin
34:48
Light

19m 38s

Intro
0:00
The Speed of Light
0:31
Speed of Light in a Vacuum
0:32
Unique Properties of Light
1:20
Lightspeed!
3:24
Lightyear
3:25
Medium
4:34
Light & Medium
4:35
Electromagnetic Spectrum
5:49
Electromagnetic Spectrum Overview
5:50
Electromagnetic Wave Classifications
7:05
7:06
Microwave
8:30
Infrared and Visible Spectrum
9:02
Ultraviolet, X-rays, and Gamma Rays
9:33
So Much Left to Explore
11:07
So Much Left to Explore
11:08
Example 1: How Much Distance is in a Light-year?
13:16
Example 2: Electromagnetic Wave
16:50
Example 3: Radio Station & Wavelength
17:55
Section 7: Thermodynamics
Fluids

42m 52s

Intro
0:00
Fluid?
0:48
What Does It Mean to be a Fluid?
0:49
Density
1:46
What is Density?
1:47
Formula for Density: ρ = m/V
2:25
Pressure
3:40
Consider Two Equal Height Cylinders of Water with Different Areas
3:41
Definition and Formula for Pressure: p = F/A
5:20
Pressure at Depth
7:02
Pressure at Depth Overview
7:03
Free Body Diagram for Pressure in a Container of Fluid
8:31
Equations for Pressure at Depth
10:29
Absolute Pressure vs. Gauge Pressure
12:31
Absolute Pressure vs. Gauge Pressure
12:32
Why Does Gauge Pressure Matter?
13:51
Depth, Not Shape or Direction
15:22
Depth, Not Shape or Direction
15:23
Depth = Height
18:27
Depth = Height
18:28
Buoyancy
19:44
Buoyancy and the Buoyant Force
19:45
Archimedes' Principle
21:09
Archimedes' Principle
21:10
22:30
22:31
Example 1: Rock & Fluid
23:47
Example 2: Pressure of Water at the Top of the Reservoir
28:01
Example 3: Wood & Fluid
31:47
Example 4: Force of Air Inside a Cylinder
36:20
Intro to Temperature & Heat

34m 6s

Intro
0:00
Absolute Zero
1:50
Absolute Zero
1:51
Kelvin
2:25
Kelvin
2:26
Heat vs. Temperature
4:21
Heat vs. Temperature
4:22
Heating Water
5:32
Heating Water
5:33
Specific Heat
7:44
Specific Heat: Q = cm(∆T)
7:45
Heat Transfer
9:20
Conduction
9:24
Convection
10:26
11:35
Example 1: Converting Temperature
13:21
Example 2: Calories
14:54
Example 3: Thermal Energy
19:00
Example 4: Temperature When Mixture Comes to Equilibrium Part 1
20:45
Example 4: Temperature When Mixture Comes to Equilibrium Part 2
24:55
Change Due to Heat

44m 3s

Intro
0:00
Linear Expansion
1:06
Linear Expansion: ∆L = Lα(∆T)
1:07
Volume Expansion
2:34
Volume Expansion: ∆V = Vβ(∆T)
2:35
Gas Expansion
3:40
Gas Expansion
3:41
The Mole
5:43
Conceptual Example
5:44
7:30
Ideal Gas Law
9:22
Ideal Gas Law: pV = nRT
9:23
p = Pressure of the Gas
10:07
V = Volume of the Gas
10:34
n = Number of Moles of Gas
10:44
R = Gas Constant
10:58
T = Temperature
11:58
A Note On Water
12:21
A Note On Water
12:22
Change of Phase
15:55
Change of Phase
15:56
Change of Phase and Pressure
17:31
Phase Diagram
18:41
Heat of Transformation
20:38
Heat of Transformation: Q = Lm
20:39
Example 1: Linear Expansion
22:38
Example 2: Explore Why β = 3α
24:40
Example 3: Ideal Gas Law
31:38
Example 4: Heat of Transformation
38:03
Thermodynamics

27m 30s

Intro
0:00
First Law of Thermodynamics
1:11
First Law of Thermodynamics
1:12
Engines
2:25
Conceptual Example: Consider a Piston
2:26
Second Law of Thermodynamics
4:17
Second Law of Thermodynamics
4:18
Entropy
6:09
Definition of Entropy
6:10
Conceptual Example of Entropy: Stick of Dynamite
7:00
Order to Disorder
8:22
Order and Disorder in a System
8:23
The Poets Got It Right
10:20
The Poets Got It Right
10:21
Engines in General
11:21
Engines in General
11:22
Efficiency
12:06
Measuring the Efficiency of a System
12:07
Carnot Engine ( A Limit to Efficiency)
13:20
Carnot Engine & Maximum Possible Efficiency
13:21
Example 1: Internal Energy
15:15
Example 2: Efficiency
16:13
Example 3: Second Law of Thermodynamics
17:05
Example 4: Maximum Efficiency
20:10
Section 8: Electricity
Electric Force & Charge

41m 35s

Intro
0:00
Charge
1:04
Overview of Charge
1:05
Positive and Negative Charges
1:19
A Simple Model of the Atom
2:47
Protons, Electrons, and Neutrons
2:48
Conservation of Charge
4:47
Conservation of Charge
4:48
Elementary Charge
5:41
Elementary Charge and the Unit Coulomb
5:42
Coulomb's Law
8:29
Coulomb's Law & the Electrostatic Force
8:30
Coulomb's Law Breakdown
9:30
Conductors and Insulators
11:11
Conductors
11:12
Insulators
12:31
Conduction
15:08
Conduction
15:09
Conceptual Examples
15:58
Induction
17:02
Induction Overview
17:01
Conceptual Examples
18:18
Example 1: Electroscope
20:08
Example 2: Positive, Negative, and Net Charge of Iron
22:15
Example 3: Charge and Mass
27:52
Example 4: Two Metal Spheres
31:58
Electric Fields & Potential

34m 44s

Intro
0:00
Electric Fields
0:53
Electric Fields Overview
0:54
Size of q2 (Second Charge)
1:34
Size of q1 (First Charge)
1:53
Electric Field Strength: Newtons Per Coulomb
2:55
Electric Field Lines
4:19
Electric Field Lines
4:20
Conceptual Example 1
5:17
Conceptual Example 2
6:20
Conceptual Example 3
6:59
Conceptual Example 4
7:28
8:47
8:48
Why Does It Work?
9:33
Electric Potential Energy
11:40
Electric Potential Energy
11:41
Electric Potential
13:44
Electric Potential
13:45
Difference Between Two States
14:29
Electric Potential is Measured in Volts
15:12
Ground Voltage
16:09
Potential Differences and Reference Voltage
16:10
Ground Voltage
17:20
Electron-volt
19:17
Electron-volt
19:18
Equipotential Surfaces
20:29
Equipotential Surfaces
20:30
Equipotential Lines
21:21
Equipotential Lines
21:22
Example 1: Electric Field
22:40
Example 2: Change in Energy
24:25
Example 3: Constant Electrical Field
27:06
Example 4: Electrical Field and Change in Voltage
29:06
Example 5: Voltage and Energy
32:14
Electric Current

29m 12s

Intro
0:00
Electric Current
0:31
Electric Current
0:32
Amperes
1:27
Moving Charge
1:52
Conceptual Example: Electric Field and a Conductor
1:53
Voltage
3:26
Resistance
5:05
Given Some Voltage, How Much Current Will Flow?
5:06
Resistance: Definition and Formula
5:40
Resistivity
7:31
Resistivity
7:32
Resistance for a Uniform Object
9:31
Energy and Power
9:55
How Much Energy Does It take to Move These Charges Around?
9:56
What Do We Call Energy Per Unit Time?
11:08
Formulas to Express Electrical Power
11:53
Voltage Source
13:38
Introduction to Voltage Source
13:39
Obtaining a Voltage Source: Generator
15:15
Obtaining a Voltage Source: Battery
16:19
Speed of Electricity
17:17
Speed of Electricity
17:18
Example 1: Electric Current & Moving Charge
19:40
Example 2: Electric Current & Resistance
20:31
Example 3: Resistivity & Resistance
21:56
Example 4: Light Bulb
25:16
Electric Circuits

52m 2s

Intro
0:00
Electric Circuits
0:51
Current, Voltage, and Circuit
0:52
Resistor
5:05
Definition of Resistor
5:06
Conceptual Example: Lamps
6:18
Other Fundamental Components
7:04
Circuit Diagrams
7:23
Introduction to Circuit Diagrams
7:24
Wire
7:42
Resistor
8:20
Battery
8:45
Power Supply
9:41
Switch
10:02
Wires: Bypass and Connect
10:53
A Special Not in General
12:04
Example: Simple vs. Complex Circuit Diagram
12:45
Kirchoff's Circuit Laws
15:32
Kirchoff's Circuit Law 1: Current Law
15:33
Kirchoff's Circuit Law 1: Visual Example
16:57
Kirchoff's Circuit Law 2: Voltage Law
17:16
Kirchoff's Circuit Law 2: Visual Example
19:23
Resistors in Series
21:48
Resistors in Series
21:49
Resistors in Parallel
23:33
Resistors in Parallel
23:34
Voltmeter and Ammeter
28:35
Voltmeter
28:36
Ammeter
30:05
Direct Current vs. Alternating Current
31:24
Direct Current vs. Alternating Current
31:25
Visual Example: Voltage Graphs
33:29
Example 1: What Voltage is Read by the Voltmeter in This Diagram?
33:57
Example 2: What Current Flows Through the Ammeter When the Switch is Open?
37:42
Example 3: How Much Power is Dissipated by the Highlighted Resistor When the Switch is Open? When Closed?
41:22
Example 4: Design a Hallway Light Switch
45:14
Section 9: Magnetism
Magnetism

25m 47s

Intro
0:00
Magnet
1:27
Magnet Has Two Poles
1:28
Magnetic Field
1:47
Always a Dipole, Never a Monopole
2:22
Always a Dipole, Never a Monopole
2:23
Magnetic Fields and Moving Charge
4:01
Magnetic Fields and Moving Charge
4:02
Magnets on an Atomic Level
4:45
Magnets on an Atomic Level
4:46
Evenly Distributed Motions
5:45
Unevenly Distributed Motions
6:22
Current and Magnetic Fields
9:42
Current Flow and Magnetic Field
9:43
Electromagnet
11:35
Electric Motor
13:11
Electric Motor
13:12
Generator
15:38
A Changing Magnetic Field Induces a Current
15:39
Example 1: What Kind of Magnetic Pole must the Earth's Geographic North Pole Be?
19:34
Example 2: Magnetic Field and Generator/Electric Motor
20:56
Example 3: Destroying the Magnetic Properties of a Permanent Magnet
23:08
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 1 answerLast reply by: Professor Selhorst-JonesThu Dec 3, 2015 10:05 PMPost by Gurwinder Chana on December 3, 2015You never talked about color which quite important, or you think that information is enough for me in light unit

### Light

• Light is extremely fast. In a vacuum, light travels at
 c=299   792   458 m s ≈ 3·108 m s .
• Depending on the material light is traveling through, its speed will change. Light travels through air close enough to c that we can use that value when working on problems.
• Since light moves so fast, we can talk about very large distances using its speed as a reference point:
 Lightyear = c ·(1 year).
• Normally waves need a medium to propagate through. This is not true of light, though. Light is able to travel without any medium (which is why the light of the sun can reach us, even though it's a wave).
• The word "light" is sort of a misnomer. The visible spectrum we are used to seeing is only part of the much larger electromagnetic spectrum that makes up light.
• Different kinds of electromagnetic waves have different frequencies. Higher frequencies carry more energy, lower frequencies carry less.

### Light

Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.

• Intro 0:00
• The Speed of Light 0:31
• Speed of Light in a Vacuum
• Unique Properties of Light
• Lightspeed! 3:24
• Lightyear
• Medium 4:34
• Light & Medium
• Electromagnetic Spectrum 5:49
• Electromagnetic Spectrum Overview
• Electromagnetic Wave Classifications 7:05
• Microwave
• Infrared and Visible Spectrum
• Ultraviolet, X-rays, and Gamma Rays
• So Much Left to Explore 11:07
• So Much Left to Explore
• Example 1: How Much Distance is in a Light-year? 13:16
• Example 2: Electromagnetic Wave 16:50
• Example 3: Radio Station & Wavelength 17:55

### Transcription: Light

Hi, welcome back to educator.com. Today we’re going to be talking about light.0000

Light is a complex phenomenon that is extremely important to a huge variety of aspects in physics and we’re not going to have enough time to fully explore it in this course.0005

Instead we’re going to be able to limit our discussion of light to ideas we can easily pull from understanding waves.0014

That’s still going to give us a much better understanding of what’s going on with light.0019

Keep in mind there is a lot of stuff to talk about in light.0023

We’ll talk about a little bit of that at the end of this. We’re still going to get some idea of what’s going on here.0027

First off, light is fast, really, really fast. In a vacuum, light travels at a rate of c equals 299,792,458 meters per second.0033

Which is approximately to equal to 3x10^8 meters per second and for the most part, all the problems that we’re going to be working on and all the problems you’ll ever have to work on, unless you get into serious, serious theoretical physics.0048

You’re going to be enough with 3x10^8 meter per second, that’s pretty much what all physicists wind up memorizing.0060

So 3x10^8 meters per second equals c, the speed of light. This value is so important it’s given its own constant, once again that’s c.0067

Speed of light, 3x10^8 meters per second and that is fast.0074

Light also has this unique property that stationary and moving observers all measure the same speed for light.0081

That’s not true for all other types of waves. Consider if we had a wave on the ocean moving at 3 meters per second this way.0088

If we were in a boat that was going at 2 meters per second, we’d wind up seeing that wave at only moving at 1 meters per second, right?0097

From our point of view, if we can’t see any stationary objects around us, we’re moving because we can’t see that fact that we’re moving if we aren’t experiencing acceleration.0105

We don’t have any reference points. So if we’re in the middle of the sea and we’re moving at a certain speed and we look down at the waves in the water underneath us.0115

It’s going to seem like its moving depending on our speed. But if on the other hand, we were going in the opposite direction.0123

We’d wind up seeing it moving at 5 meters per second, right? So the experience would be 1 meter per seconds if we were going with it, 5 meters per second if we were going against it.0132

If we’re sitting still in the water, it’d be 3 meters per second.0141

For light, it has the phenomenon that for every direction you’re moving, you record the exact same speed.0144

That is fantastically interesting. That’s so different from all other types of waves, it’s just…it’s really interesting, really important.0151

Also what we’re going to wind up…what we’re not where going to wind up looking at, but one of the cornerstones of relativity is this fact.0160

This doesn’t mean that light travels through all materials at equals rates though.0170

In a vacuum, light travels at c and it travels very close to sea through air, like we talked about before, c for a vacuum.0174

In water, it travels at 0.75 c. Through glass, 0.67 c. Through diamond at 0.4 c.0180

Still really, really fast but it does mean when its moving through another material, it winds up being slowed down.0188

It’s able to move at its full speed in a perfect vacuum, but as it winds up having to encounter other objects to pass through, it’s not able to keep up its speed quite as much.0195

Light speed. Since light moves so fast and it’s so important to the nature of the universe, occasionally we talk distance using the speed of light.0205

If we’re talking about astronomical stuff, it’s a really great thing to be able to talk about, because we’re talking about really, really large distances in space.0212

So being able to talk about how far light manages to travel in year, we’re able to talk the speed of light times the time of one year.0219

Multiply it by the time of one year, we’re able to talk about a light year.0226

A light year is a measurement of distance because it’s how far light could travel in on year.0229

For large, large distances in space being able to talk about the distance in terms of light years is a really handy thing to be able to talk about.0236

It also tells us how long it would take for information from that galaxy to make it to us, because of its sun, its sun for example goes supernova and explodes but its 50 light years away from us.0243

We’re not going to be able to get the information of it exploding, the light of its explosion isn’t going to get to us until 50 years after it explodes.0255

Some of the information we’re getting, some of the stars we see in the sky could actually wind up being dead stars, we just don’t know they’re dead yet because we haven’t seen the information of their explosion come to us yet or their nullification in some way.0261

Medium. Normally a wave needs a medium to propagate through. If we have waves and water, we need the water to be able to move up and down.0275

If we have a wave in a string, we need the string to whip up and down.0283

Me speaking needs this air for it to be able to bounce against and have those differentials.0286

Light on the other hand needs no such medium. Light is able to move through a vacuum without issue.0290

Nobody else can do that. If there’s nothing there, other waves can’t transmit themselves because they don’t have anything to vibrate against, they don’t have anything to move.0296

Light is in itself its own motion. It’s its own medium. We’re starting to get into a complicated thing here about the dual particle wave nature of light, so we’re not going to talk too much about this.0306

But light suffices to say doesn’t need a medium, it’s able to just go on its own.0319

Unlike all the other kinds of waves that we learned about. Now notice the speed can still be affected by what it travels through.0324

Remember if you’re traveling through diamond, you go slower. You travel through water, you go slower.0329

It’s not the same as that material being what’s transmitting the wave.0333

It’s traveling through the water doesn’t mean that the water’s motion is what moves the wave along.0337

The wave is able to go through the water but then also hop out to going through just pure raw vacuum.0342

It’s a really big difference.0346

Electromagnetic spectrum. Light is kind of a misnomer and me using the word light; we want to expand that to more than just the light.0350

Just the light that you’re seeing me with. There is way more quote on quote light than just the light that you’re seeing me with.0358

The light that we see, visual light is only one of many forms of light.0364

Light is really just part of the electromagnetic spectrum.0369

The EM’s spectrum is a really wide set of possibilities. It’s going to go over a huge amount and we’ll talk about some of those.0373

Visible light, the light that we see, is just a small fraction of the EM spectrum.0380

There is many more possibilities and it’s those other possibilities that allow us to transmit other kinds of information.0385

We’ll talk about that in a little bit. Any electromagnetic wave, they share many similarities for every electromagnetic wave.0390

Such as their speed and their ability to move without a medium. Different frequencies and wave lengths give some different properties though, such as the amount of energy that the wave carries.0397

A higher frequency has more energy because that means that it’s vibrating more.0404

If we had a string for example and I whipped it up and down only once a second, I’d have way more energy in that string if I was whipping it up and down a hundred times per second right?0408

There’d be more energy being put into it and a similar idea is happening with waves.0416

More energy is in the higher frequencies because they’re vibrating more.0420

The different classifications for electromagnetic waves.0427

So the long radio wave has a frequency of anywhere from 10^0, so just 1 hertz to 10^5 hertz.0430

Radio waves, the kind of stuff we use to send television or cellphones or…cellphones actually start to verge into microwaves depending…well anyway, there’s a lot of different possibilities in different sections of the spectrum.0439

Radio waves, we use to send radio as you might guess. We used to send, I believe radar, I’m not actually sure about that, don’t hold me to it.0455

We definitely use to send television. A lot of information gets transmitted from place to place.0464

Because by the way that we move the wave by taking slight variations off that frequency we can send that light, quote on quote light, we can send those electronic, those electromagnetic waves through a space.0469

Say from the top of a mountain with a transmitter to a city that has a radio in it.0482

We’re able to put out a certain kind of electromagnetic spectrum and by vibrating slightly different than the expected frequency, that radio on the other end is able to pick up those slightly different vibrations and turn that into some sort of information.0486

Like say sound information that it then puts out through a speaker.0502

Those slight variations off of the starting base level put out information, right?0505

Microwave, the same sort of thing that you in a microwave is 10^9 to 10^11 hertz.0510

The reason why that works even though they’re lower energy waves than the visual spectrum.0517

We’re able to have it putting out energy because it’s able to sync to the appropriate frequency that water and sugars and many kinds of fats, that they’re on so that it’s able to vibrate them and cause them to pick it up and have a resonate frequency as we talked about before.0521

And able to increase the vibrations in those atoms, thus increasing the energy, the heat in it.0537

Infrared, 10^12, 10^14. Visual spectrum, see how small it is, it’s just from 4x10^14 to 7.9x10^14 hertz.0542

ROYGBIV. Red, orange, yellow, green, blue, indigo, violet.0551

Haven’t put down the specific times, if you want to know more, easy to look up.0557

As it cycles up, we go from red up to violet as we go through higher and higher frequencies.0560

That’s why it’s called infrared, below red and for the next energy above it, ultraviolet, above violet.0567

More than that we get ultraviolet 10^15, 10^16.0574

X-rays, even more and finally gamma rays covers the really extreme high, high, high frequency. Really high energy things.0579

Now the reason that ultraviolet rays, x-rays, gamma rays, though you’re really unlikely to be exposed to those.0585

The reason why these can be potentially damaging to us is there is such high energy things and they have such a small wave length.0594

They’re able to pierce through our body and they’re able to hit a cell and they’ve got enough energy in them to be able to potentially cut off a piece of DNA.0598

Cut DNA in a certain way. Potentially, if you’re really unlikely, that DNA will be cut in just the wrong way, and this happening to you lots of times.0607

You get exposed to a lot of ultraviolet light, suddenly you’re exposed to more possibility of skin cancer.0615

You get exposed x-rays, suddenly you’re exposed to the possibility of maybe getting some kind of cancer inside of yourself.0620

There is a lot of other things that cause other carcinogens out there, but this one possible way to get cancer is because DNA winds up getting split.0625

So suddenly the code that tells the cell how to behave, how to multiply, goes haywire and most of the time the cell fails to work at all and just dies.0633

Sometimes it manages to get cut in the quote on quote right way, not right at all, very bad from our point of view.0643

Cut in just the wrong way and suddenly it goes haywire, goes out of control and it starts to produce many, many of itself and we get a cancer.0649

It does something bad to the body. The reason why that’s possible is because we’ve got such high energy in them that they’re able to actually effect ourselves and they’re able to potentially do things to our DNA.0656

Now there’s huge amounts left to explore. We could talk more, I mean that idea that I was just talking about; x-rays and ultraviolet and gamma rays being able to cause cancer damage to cells.0668

So much we could talk about just in that tiny little idea, but there is way more things here.0679

We’ve just begun to talk about the tip of the iceberg in terms of light.0682

There is so much more. We could fill many college physics’ courses and then more onto a lifetime of research after this.0686

Huge amount of things. Some of the topics you might one day encounter if you’re interested in light and there is lots to be interested in about.0693

Just go ahead, search for yourself. You find out all sorts cool ideas or go ahead and take more courses.0698

This is…I mean there’s all sorts of cool things in physics and this is one of them.0703

First off, optics, how light behaves with various materials.0705

The way light is going to move through them, pass through them. Change, be reflected.0709

The energy in light, we started to talk about there is more energy in light and less energy in different things but we didn’t get into any specific numbers.0713

Way more to be talked about there. The fact that energy in light, not energy in light.0720

Light can both be treated simultaneous as wave and as partially.0725

You’ve probably heard of photons, that’s a single packet of light.0728

Light behaves, light has some of the effects of a wave. It has those interference effects that we’ve talked about previously with waves.0732

The same time it also can be broken down into discretized quantities of single chunks.0739

It’s got a really strange thing going on there. We don’t normally thing of a wave as something that can broken up into a single piece.0743

Light able to do both at once. Once again, really unique phenomenon.0749

Finally, all of relativity. Everything in relativity is based on this fact that light is this unique thing and that light is top speed limit of the universe.0753

And why that is a whole kettle of fish to get into. There is huge amounts of stuff here.0765

Light is interesting. Still at least we’ve managed to crack up an amazing new vista to be interested in and we’ve dipped our toes.0769

We’ve got some new ideas and it helped us understand our universe just a little bit more and it’s a really cool thing.0777

I’d really encourage you, go ahead, just do some research. Get yourself exposed to a whole bunch of ideas.0783

You’ll get the chance if you want to, to start taking more courses or just do some personal reading and you can learn a lot about what’s going on in the world and the universe.0788

I mean everything at once. Alright, ready for some examples.0794

How much distance is in a light year?0798

We start off, we know the speed of light, right? C is equal to 3x10^8 meters per second.0800

We’ve got that down. If we want to know what distance is covered, we need to know how much time is in a year.0805

If time is equal to 1 year. Well 1 year is equal to 365.25 days. We’ve got that leap year every four years.0811

We’ve got a quarter of a year in there, so 365.25 days.0820

If we want to know how many hours are in there, 365.25 times 24 hours in a day.0826

We get that we’ve got 8,766 hours in a year.0839

Which means that we can multiply that by 60 and we’ll get how many minutes are in a year, 525,960 minutes.0846

Which we could turn into seconds. We can multiply that number by another 60 seconds.0863

We’re going to get 3.156 x 10^7 seconds.0872

If we want to know what the distance that it covers, we just put the two together.0879

Distance equals velocity times time. So the velocity of our thing is 3 x 10^8 and we multiply that by the time that it has to travel, 3.156 x 10^7 seconds.0882

We get a distance of 9.467 x 10^15 meters. That is a huge, huge distance.0894

10^6 means that we’re dealing…so 10^3 means we’re dealing with thousands.0908

10^6 means we’re dealing with millions. 10^9 means that we’re dealing with billions.0913

10^12 means that we’re dealing with trillions. 10^16 means that we’re dealing with quadrillions.0918

That’s almost 1 quadrillion meters. That’s a massive amount of distance, this is just a huge amount of distance that we’re able to cover.0925

Now keep in mind that the closest star system to us, Alpha Centauri is approximately 4.3 light years away.0933

We’re dealing with an absolutely massive amount of distance between us and that other system.0942

If we want to get there in any reasonable amount of time, we’re going to have to figure out some way to get a close approximation to the speed of light.0948

Once again to relativity, you start to realize that getting into reasonable amounts of speed like that, really, really difficult and there is even more complex stuff going on there.0954

Just even moving at 1/10th the speed of light, think about how much energy you’d have to put into that.0964

Moving at 1/10th the speed of light, 3 x 10^7. If we’re dealing classical mechanics, that would be 3 x 10^7, the whole thing squared times ½ times the mass of the object.0970

½ mv squared. Huge, huge, huge amount of energy.0983

To be able to get any sort of space ship to any other solar system is going to require some incredible feat of engineering or some incredible feat of scientific process for us to be able to cover these huge distances.0989

Right now we’re basically in the solar system for at least a while longer.1000

Being able to actually touch the other stars is going to take something really, really cool and really, really smart from humanity.1004

Example two. If we perceive an electromagnet wave at the color green it’s going to have something…so we perceive a 525 nanometer wave if it’s moving through the air at the color green.1011

What frequency is that? Remember electromagnetic waves very near to sea and air.1023

Remember, we know that the speed of a wave to equal to its frequency times its wave length.1027

If we’ve got the speed of the wave at 3 x 10^8 and we want to know what the frequency is.1035

Well we know the wave length, 525 nanometers. So 525 x 10^-9 meters.1043

Now we can easily just solve for frequency. So frequency is equal to 3 x 10^8 / 525 x 10^-9 which is equal to 5.71 x 10^14 hertz.1050

Smack dap in the middle of that ROYGBIV spectrum, right in where G is going to be.1065

That’s what the frequency that we’d wind up getting out of that wave.1071

Now say you want to tune into my favorite radio station, KSBC at 88.7 megahertz.1076

If KSBC is at 88.7 megahertz, which it is, what wave length does that mean you’d have to be scanning for?1081

If you’re scanning for KSBC at 88.7 megahertz what wave length would that mean that we’re looking to be able to pick up?1089

Well once again we use the exact same thing just slightly different.1097

Frequency times wave length. Well the velocity we’re dealing with electromagnetic waves is 3 x 10^8 equals whatever frequency it is, so in this case 88.7 megahertz.1100

88.7 x 10^6 hertz because it’s mega. Times the wave length, so the wave length is going to be equal to 88.7…oh whoops, sorry, put that the wrong way on.1111

3 x 10^8 / 88.7 x 10^6. Which means that we’re going to be looking for a wave length that’s 3.38 meters.1125

That’s pretty big. It’s really interesting to compare how much difference there was between the wave length of that green light.1138

Tiny, tiny thing. 525 nanometers to 3.38 meters. That’s practically two of me standing on my shoulders.1145

That’s a really tall wave length. That means if you’re going to want to pick it up, you’re got to have some way of being able to see all that information in that really long wave length passing by you.1152

Which has to do with the way waves work, but we once again aren’t going to quite get into that.1160

3.38 meters, really long wave length because it’s got a really small frequency compared to some of the other ones.1165

Alright, hopefully that gives you some idea of how light works and possibly spark your interest in some of the many, many interesting…1170

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