When you think about light bouncing off of mirrors it of course bounces at the angle that it came in at. Law of reflection says incident angle equals reflected angle. But what if we have two mirrors at right angles? Okay, so let's take a mirror. And let's take a second mirror and put it right next to the first. And we'll put them at right angles to each other. Okay? So we've made this nice sort of assortment of mirrors here. What happens when a ray comes in? A ray comes in and it bounces off the first surface. And we know that it bounces at the same as its incident angle. And so it's going to look something like that. When it bounces off the second mirror it's going to bounce at an angle like so. And to make this really convenient let's do the following. Let's say that this angle is 45 degrees. And if that angle is 45 degrees then this angle is 45 degrees. Okay, and if those two angles are 45 degrees then those two angles are also 45 degrees. Okay everything adds up. The outgoing ray is in fact parallel to the incoming ray. You might have seen these before, okay. They have these in dressing rooms. And the reason that they put these in dressing room sometimes it's so that you can see your reflection the way other people see it. The bounce off the first mirror flips you from left to right. The bounce off the second mirror flips you back, right to left. So if you stand in front of one of these mirrors and you raise your right hand your image raises its right hand. It's a very nice way to see what you look like but there's a much more important feature here, which is the following. Let's say we didn't just do this in two dimensions. Let's say we did it in three dimensions. If you do it in three dimensions it's called a corner cube and let's see if we can draw it out. Okay, these are the mirror surfaces. And now any incoming ray will bounce three times and come out parallel. And this thing is called a corner cube. This last ray took a little funny jog there. Straighten that out a bit. Okay, it's called a corner cube. And it's used in physics quite a lot. But, you are in fact familiar with this device. Okay, I can guarantee you that at some point today, you have come across a corner cube in your regular daily life. Where have you seen one of these things? Where have you seen a corner cube at some point today? All right? The answer is anywhere you see a reflector like on a bike. Okay, a bike reflector has a whole bunch of little tiny corner cubes in it. All right? Why is that? Well, let's think about what happens. When you're driving in your car Here you are, sitting in your car. Okay, and you're looking out the front of your car. And my car is looking a little backwards, but that's okay. Here you are. These are the headlights on your car. Right here. When you're driving at night, and somebody comes by on their bicycle you would like to be able to see them. Okay, so here is the bike. Person riding along. Happy as can be. On the wheels of their bike, they have these little reflectors. And in that reflector are a whole bunch of these little tiny corner cubes. So, what's the point? The point is this. Light from your headlights will hit that reflector and it will come back on itself. Almost exactly. A little bit off. When it comes back, it just skims over the hood of your car past your headlights and comes to your eyeball. Okay? So that's the whole point of those bike reflectors. Take those headlights send it back to the person driving the car they can then see that it belongs to a bicycle. So it's kind of weird when you think about you're in your car. If somebody is in the car next to you and they have their headlights off they can't see the bike reflector. Okay? Only you can see the bike reflector because those headlights are coming straight back to you. They're not going to other people, they're coming straight back to you. So there's one more place where corner cubes are located. And this is very exciting, okay. They are located on the moon. Way back in the early 70s the Apollo astronauts went up to the moon right, when we "went to the moon" and they brought a whole bunch of mirrors with them. They brought a whole bunch of corner cube reflectors and they put them on the surface of the moon. And the idea was we're going to use these someday, for something important. And guess what? We are using them today for something important. We are taking these big lasers, just like these headlights, shining it at the mirrors on the moon and collecting the light that comes back down to us. And when we do that we can determine very precisely the distance from the earth to the moon. We know how fast light goes. We now know how long it takes in time to go there and back. And so you can measure the distance very precisely to the moon. And there was a talk recently about this and the precision of that measurement currently is 0.8 millimeters. We know the distance from the earth to the moon to within 0.8 millimeters. Which is sort of remarkable, when you think about it.
Table of contents
- 0. Math Review31m
- 1. Intro to Physics Units1h 23m
- 2. 1D Motion / Kinematics3h 56m
- Vectors, Scalars, & Displacement13m
- Average Velocity32m
- Intro to Acceleration7m
- Position-Time Graphs & Velocity26m
- Conceptual Problems with Position-Time Graphs22m
- Velocity-Time Graphs & Acceleration5m
- Calculating Displacement from Velocity-Time Graphs15m
- Conceptual Problems with Velocity-Time Graphs10m
- Calculating Change in Velocity from Acceleration-Time Graphs10m
- Graphing Position, Velocity, and Acceleration Graphs11m
- Kinematics Equations37m
- Vertical Motion and Free Fall19m
- Catch/Overtake Problems23m
- 3. Vectors2h 43m
- Review of Vectors vs. Scalars1m
- Introduction to Vectors7m
- Adding Vectors Graphically22m
- Vector Composition & Decomposition11m
- Adding Vectors by Components13m
- Trig Review24m
- Unit Vectors15m
- Introduction to Dot Product (Scalar Product)12m
- Calculating Dot Product Using Components12m
- Intro to Cross Product (Vector Product)23m
- Calculating Cross Product Using Components17m
- 4. 2D Kinematics1h 42m
- 5. Projectile Motion3h 6m
- 6. Intro to Forces (Dynamics)3h 22m
- 7. Friction, Inclines, Systems2h 44m
- 8. Centripetal Forces & Gravitation7h 26m
- Uniform Circular Motion7m
- Period and Frequency in Uniform Circular Motion20m
- Centripetal Forces15m
- Vertical Centripetal Forces10m
- Flat Curves9m
- Banked Curves10m
- Newton's Law of Gravity30m
- Gravitational Forces in 2D25m
- Acceleration Due to Gravity13m
- Satellite Motion: Intro5m
- Satellite Motion: Speed & Period35m
- Geosynchronous Orbits15m
- Overview of Kepler's Laws5m
- Kepler's First Law11m
- Kepler's Third Law16m
- Kepler's Third Law for Elliptical Orbits15m
- Gravitational Potential Energy21m
- Gravitational Potential Energy for Systems of Masses17m
- Escape Velocity21m
- Energy of Circular Orbits23m
- Energy of Elliptical Orbits36m
- Black Holes16m
- Gravitational Force Inside the Earth13m
- Mass Distribution with Calculus45m
- 9. Work & Energy1h 59m
- 10. Conservation of Energy2h 51m
- Intro to Energy Types3m
- Gravitational Potential Energy10m
- Intro to Conservation of Energy29m
- Energy with Non-Conservative Forces20m
- Springs & Elastic Potential Energy19m
- Solving Projectile Motion Using Energy13m
- Motion Along Curved Paths4m
- Rollercoaster Problems13m
- Pendulum Problems13m
- Energy in Connected Objects (Systems)24m
- Force & Potential Energy18m
- 11. Momentum & Impulse3h 40m
- Intro to Momentum11m
- Intro to Impulse14m
- Impulse with Variable Forces12m
- Intro to Conservation of Momentum17m
- Push-Away Problems19m
- Types of Collisions4m
- Completely Inelastic Collisions28m
- Adding Mass to a Moving System8m
- Collisions & Motion (Momentum & Energy)26m
- Ballistic Pendulum14m
- Collisions with Springs13m
- Elastic Collisions24m
- How to Identify the Type of Collision9m
- Intro to Center of Mass15m
- 12. Rotational Kinematics2h 59m
- 13. Rotational Inertia & Energy7h 4m
- More Conservation of Energy Problems54m
- Conservation of Energy in Rolling Motion45m
- Parallel Axis Theorem13m
- Intro to Moment of Inertia28m
- Moment of Inertia via Integration18m
- Moment of Inertia of Systems23m
- Moment of Inertia & Mass Distribution10m
- Intro to Rotational Kinetic Energy16m
- Energy of Rolling Motion18m
- Types of Motion & Energy24m
- Conservation of Energy with Rotation35m
- Torque with Kinematic Equations56m
- Rotational Dynamics with Two Motions50m
- Rotational Dynamics of Rolling Motion27m
- 14. Torque & Rotational Dynamics2h 5m
- 15. Rotational Equilibrium3h 39m
- 16. Angular Momentum3h 6m
- Opening/Closing Arms on Rotating Stool18m
- Conservation of Angular Momentum46m
- Angular Momentum & Newton's Second Law10m
- Intro to Angular Collisions15m
- Jumping Into/Out of Moving Disc23m
- Spinning on String of Variable Length20m
- Angular Collisions with Linear Motion8m
- Intro to Angular Momentum15m
- Angular Momentum of a Point Mass21m
- Angular Momentum of Objects in Linear Motion7m
- 17. Periodic Motion2h 9m
- 18. Waves & Sound3h 40m
- Intro to Waves11m
- Velocity of Transverse Waves21m
- Velocity of Longitudinal Waves11m
- Wave Functions31m
- Phase Constant14m
- Average Power of Waves on Strings10m
- Wave Intensity19m
- Sound Intensity13m
- Wave Interference8m
- Superposition of Wave Functions3m
- Standing Waves30m
- Standing Wave Functions14m
- Standing Sound Waves12m
- Beats8m
- The Doppler Effect7m
- 19. Fluid Mechanics2h 27m
- 20. Heat and Temperature3h 7m
- Temperature16m
- Linear Thermal Expansion14m
- Volume Thermal Expansion14m
- Moles and Avogadro's Number14m
- Specific Heat & Temperature Changes12m
- Latent Heat & Phase Changes16m
- Intro to Calorimetry21m
- Calorimetry with Temperature and Phase Changes15m
- Advanced Calorimetry: Equilibrium Temperature with Phase Changes9m
- Phase Diagrams, Triple Points and Critical Points6m
- Heat Transfer44m
- 21. Kinetic Theory of Ideal Gases1h 50m
- 22. The First Law of Thermodynamics1h 26m
- 23. The Second Law of Thermodynamics3h 11m
- 24. Electric Force & Field; Gauss' Law3h 42m
- 25. Electric Potential1h 51m
- 26. Capacitors & Dielectrics2h 2m
- 27. Resistors & DC Circuits3h 8m
- 28. Magnetic Fields and Forces2h 23m
- 29. Sources of Magnetic Field2h 30m
- Magnetic Field Produced by Moving Charges10m
- Magnetic Field Produced by Straight Currents27m
- Magnetic Force Between Parallel Currents12m
- Magnetic Force Between Two Moving Charges9m
- Magnetic Field Produced by Loops and Solenoids42m
- Toroidal Solenoids aka Toroids12m
- Biot-Savart Law (Calculus)18m
- Ampere's Law (Calculus)17m
- 30. Induction and Inductance3h 37m
- 31. Alternating Current2h 37m
- Alternating Voltages and Currents18m
- RMS Current and Voltage9m
- Phasors20m
- Resistors in AC Circuits9m
- Phasors for Resistors7m
- Capacitors in AC Circuits16m
- Phasors for Capacitors8m
- Inductors in AC Circuits13m
- Phasors for Inductors7m
- Impedance in AC Circuits18m
- Series LRC Circuits11m
- Resonance in Series LRC Circuits10m
- Power in AC Circuits5m
- 32. Electromagnetic Waves2h 14m
- 33. Geometric Optics2h 57m
- 34. Wave Optics1h 15m
- 35. Special Relativity2h 10m
33. Geometric Optics
Reflection of Light
Video duration:
7mPlay a video:
Related Videos
Related Practice