Speed of light The speed of light is 3.0 x 108 m/s in a vacuum 3.0 x 108 m/s = 300 000 000 m/s But what does that even mean?

Speed of Light A passenger jet travels at about 900 km/h (250 m/s) It would take a jet 45 hours to fly around the world at the equator (and that’s not including time to refuel)

Speed of Light If we could move at the speed of light, we could circle the earth 7.5 times in one second

Speed of light Okay, but I say the speed of light is 3.0 x 108 m/s in a vacuum Why did I say “in a vacuum”? ?

Imagine This... Think, Pair, Share

Refraction The bending or change in direction of light when it travels from one medium to another.

angle of incidence incident ray medium A medium B refracted angle of refraction

https://www.youtube.com/watch?v=yfawFJCRDSE

Refraction “Lab” Air to plastic Water to Air Fill in the following table Make a conclusion that summarizes the result Water to Air How do the light rays change when water is added to the container? Is this similar or different to the light rays moving from air to plastic? Justify your answer? Do all the rays get refracted? Angle of incidence Angle of Refraction

The Speed of Light It’s 3.0 x 108 m/s ... isn’t it?

Less friction (less dense) More friction (more dense)

Less friction (less dense) This wheel slows down, but the others continue to move at the same speed More friction (more dense)

More friction (more dense) Less friction (less dense)

More friction (more dense) This wheel speeds up, but the others continue to move at the same speed Less friction (less dense)

Both front wheels slows down. Less friction (less dense) More friction (more dense) Both front wheels slows down.

Rules of Refraction The incident ray, refracted ray, and the normal are all on the same plane. The incident ray and the refracted ray are on opposite sides of the line that separates the media. The light bends towards the normal when the speed of the light in the second medium is less than the speed of light in the first medium.

Medium A Medium B Which medium: Is less dense? Has a higher index of refraction? Is the light traveling slower?

1 2 More Dense Larger Index

3 More Dense Larger Index 4

3 Same Density Same Index 1

The Index of Refraction (n) The ratio of the speed of light in a vacuum (c) to the speed of light in a medium (v)

Example #1 How fast does light travel through water? (The index of refraction of water is 1.33)

Example #1 How fast does light travel through water? (The index of refraction of water is 1.33) c = 3.00 x 108 m/s n = 1.33 v = ? v = 2.25x 108 m/s

Example #2 If the speed of light in a medium is 2.05 x 108 m/s, which solid medium is light traveling through?

Example #2 If the speed of light in a medium is 2.05 x 108 m/s, which solid medium is light traveling through? c = 3.00 x 108 m/s v = 2.05 x 108 m/s n = ? n = 1.46 The medium is quartz

Lateral Displacement Air Air Water Lateral Displacement

Think about it If you place two pieces of glass beside each other and shone a light through them, which way would the light bend? Towards the normal Away from the normal It would not bend It depends on the index of refraction

Think about it If you place two pieces of glass (with the same index of refraction) beside each other and shone a light through them, which way would the light bend? Towards the normal Away from the normal It would not bend

Partial Reflection and Refraction Refraction is often accompanied by reflection. Some light is reflected off of the surface and the rest is refracted. We often observe this in water, windows, and sunglasses.

Total Internal Reflection Critical Angle Air Water Total internal reflection

Total Internal Reflection Critical angle: The angle of incidence that results in an angle of refraction of 90º. Total Internal Reflection: occurs when the angle of incidence is equal or greater than the critical angle.

Total Internal Reflection Total internal reflections occurs when two conditions are met: Light is travelling more slowly in the first medium than in the second The angle of incidence is large enough that no refraction occurs

Critical Angle 48.8º 70º 25º

Fibre Optics

Questions Why don’t we use a simple plane mirror for car side mirrors? Why don’t we use plane mirrors instead of retroreflectors What properties make fibre optics useful? How do we use them?