1. UG: Describe the Nature of Electromagnetic Waves
AKA “LIGHT”
Made up of Electric & Magnetic Fields
Does NOT require a medium to travel through
All EM waves travel through a vacuum at the same speed (light speed) (Mech. Waves need a medium)
Transverse Waves
ALL EM Waves are LIGHT Waves
However, not all light is Visible

2. UG: Describe the Nature of Electromagnetic Waves
The Nature of Light
Light sources radiate energy in all directions
No medium is required (light can travel through space)
Rays of Light
Wave Fronts
Waves actually exist through space

3. UG: Describe the Origin of Electromagnetic Waves
Starts with an
accelerating electron
E Field perpendicular to B Field
Both perpendicular to direction of travel
Discuss EM Waves carry energy and NEVER END. Light we see is old, like looking back into time. Also, as NRG travels forever, it spreads out. Can look at a distant star w/ no eye damage but not our sun.// Changing E-field via moving an charge. Changing B field via moving a magnet. All together, one propagates the other forms an EM Wave.
How to Create an EM wave
A Changing E Field produces a changing B Field
A Changing B Field produces a changing E Field
This produces Electromagnetic Radiation (EM Wave)

4. UG: Describe the Nature of Electromagnetic Waves
The Electromagnetic
SPECTRUM
High Energy
Which color has the longest
wavelength? Highest Frequency?
Frequency
PSRT
IR Sensor
Demo
Discuss arbitrary divisions b/t types of light based on frequency
R Sensor Demo: Pasco IR Sensor Have Ss challenge one another to who can warm up their hands the most
UV: Use UV Light
Phosphorescent Sheet with Violet Laser
While most photoluminescent materials allow their excited electrons toquickly return to a ground state, phosphorescent materials trap their electrons in a higher energy state for minutes or even hours.
Roy G Biv
UV Light
Demo
Low Energy
Phosphorescence
Demo

5. UG: Determination of Light Speed
The Speed of Light
In 1926, American Albert Michelson verified Maxwell’s predictions from the late 1800s
Speed (c) =
± x 108 m/s
186,000 miles per second
PSRT
Maxwell’s one speed for E & B energy conservation

6. Speed of Light 186,000 miles per second 11,160,000 miles per minute
669,600,000 miles per hour

7. UG: Determination of Light Speed
ENERGY of EM Waves
Previously, Energy was dependant on Speed:
KE = ½ mv2
Light (photons) has no MASS, so energy is not dependent on speed
Energy is proportional to FREQUENCY
Does Light carry any Energy?
It’s an EM Wave – so by def. Waves carry energy. Consider warmth of the Sun … that’s energy

8. It’s an EM Wave – so by def. Waves carry energy
It’s an EM Wave – so by def. Waves carry energy. Consider warmth of the Sun … that’s energy

9. V=f Calculate the wavelength of radio waves broadcast at 107.5 MHz
An EM wave has a wavelength = 1.4 meters. What type of radiation is it?
The infrared region has a frequency range of …?
2.79 m
V=f
Low Energy
High Energy

10. Speed of Light 186,000 miles per second 11,160,000 miles per minute
669,600,000 miles per hour

11. UG: Determination of Light Speed
ENERGY of EM Waves
Previously, Energy was dependant on Speed:
KE = ½ mv2
Light (photons) has no MASS, so energy is not dependent on speed
Energy is proportional to FREQUENCY
Does Light carry any Energy?
It’s an EM Wave – so by def. Waves carry energy. Consider warmth of the Sun … that’s energy

12. It’s an EM Wave – so by def. Waves carry energy
It’s an EM Wave – so by def. Waves carry energy. Consider warmth of the Sun … that’s energy

13. V=f Calculate the wavelength of radio waves broadcast at 107.5 MHz
An EM wave has a wavelength = 1.4 meters. What type of radiation is it?
The infrared region has a frequency range of …?
2.79 m
V=f
Low Energy
High Energy

14. UG: Determination of Light Speed
PHOTONS

15. Photon – Fundamental particle of visible light

16. UG: The Reflection of Light
Light Echoes

17. UG: Describe the Nature of Reflection
The Reflection of Light
- The reason you see objects
- Interference Patterns produced

18. UG: Describe the Nature of Reflection
The Reflection of Light
Demo
= the "Normal"
Angle measured from the Normal
Incident angle,
= Reflected angle
Law of
Reflection
SUNY

19. UG: Describe the Nature of Reflection
Law of Reflection
Incident angle,= Reflected angle
Light reflects as follows =
All reflections obey the
same principle
Photo

20. UG: Describe the Nature of Reflection
What / Who do you see in the mirror?
Does it obey the Law of Reflection?
Hold a flat mirror up in the front of the room. Asks Ss who they see in the mirror. They will see other students except those directly in front of the mirror. Those they see should obey the Law of Reflection.

21. UG: Describe the Nature of Reflection
See the long beam due to the wavy nature of the water, and specular reflection. (Many places the reflection is seen). See this reflection of the moon everywhere as you long along the beach. Reason: Light source is so far away, as you walk, have not significantly changed the orientation. For a very large area, the moon is “straight across”.

22. UG: Describe the Nature of Reflection
Practice
Draw the reflected ray & compute the angle of reflection
What’s he looking at?
Flippers!
r= 300
i= 300
600

23. UG: Describe the Nature of Reflection
When you look into a plane (flat) mirror, you see an image of that has three properties:
1) The image is upright.
2) The image is the same size as you are.
3) The image is located as far behind the mirror as you are in front of it.

24. UG: Describe the Nature of Reflection
Images formed by the
Reflection of Light
Images are Front / Back Reversed
“Can you Read this” transparency backwards on the overhead shown onto the screen. Then, using a mirror, reflect it onto the ceiling. It is now readable. (We’re not projecting a virtual image….we’re redirecting a real image)

25. UG: Describe the Nature of Reflection
Images formed by the
Reflection of Light
Directions – Construct the image of the following objects in front of a plane mirror.
Graph Paper
Use Graph paper in favor of white boards d0 di

26. UG: Describe the Nature of Reflection
Images formed by the
Reflection of Light
Directions – Construct the image of the following objects in front of a plane mirror. d0 di

27. UG: Describe the Nature of Reflection
Images formed by the
Reflection of Light
Directions – Construct the image of the following objects in front of a plane mirror. S S
Front - Back Reversal d0 di

28. The Refraction of Light
When light encounters a boundary, part of the ray is reflected and the rest is refracted

29. The Refraction of Light
Refraction means: Rays of light passing through a medium are laterally displaced

30. Incident Ray
Reflected Ray
Refracted Ray

31. 2 depends on 1. 1 2. the optical densities of the two media

32. The Index of Refraction
(PSRT)
If I increase v, then my n should get…
Material
Index (n)
Speed of light
Vacuum
1.00
3 x 108 m s-1
Air
1.003
???
Water
1.33
Diamond
2.42

33. When a wave-ray passes from one medium into another it will bend due to the difference in SPEED between the two mediums.
Slow  Fast
Bends AWAY FROM NORMAL
λ INCREASES
Fast  Slow
Bends TOWARD NORMAL
λ DECREASES
Incident
Ray
Normal
Medium 1
Wave
Fronts
FAST
SLOW
Medium 2
Refracted
Ray

34. Why it slows down…
Refraction index is caused by the molecules in a medium. Air has very spread out molecules which does spread out the light molecules when it makes contact which is why light travels slower. A liquid, specifically water has more compact molecules which means the light molecules will travel even more slower.
Simplified: It depends on what the molecule makeup is of that medium.

35. If light enters a more dense medium
Bends closer to the normal!

36. Light entering a less dense medium
It bends away from normal

37. n1 and n2 = indices of refraction
Snell’s Law
The mathematical relationship that determines the refraction of light
n1 sinθ1 = n2 sinθ2
n1 and n2 = indices of refraction
θ1 = angle of incidence
θ2 = angle of refraction

38. The Refraction of Light
Formulas for Refraction

39. Find the angle of refraction!
n1sinθ1= n2sinθ2
1sin(45) = 1.33sin(x)

40. Find the angle of refraction
n1sinθ1= n2sinθ2
1.52sin(x) = 1.33sin(53.9)

42. Ex. Speed of light in Diamond is 1. 23966 E8
Ex. Speed of light in Diamond is E8. It enters a new material and speeds up to E8 m/s. What material is it?

43. Dispersion White light is made up of all visible wavelengths
Dispersion is when one beam of light comes in and separates
How? Because the light is getting separated by wavelength size.

44. If 2 = 38o calculate 1
Speed of light in water
n = 1.00
n = 1.33
38o