1. ISNS 3371 - Phenomena of Nature
The Doppler Effect - Wavelength Shift Due to Motion.
Each circle represents the crests of sound waves going in all directions from the train whistle. The circles represent wave crests coming from the train at different times, say, 1/10 second apart. If the train is moving, each set of waves comes from a different location. Thus, the waves appear bunched up in the direction of motion and stretched out in the opposite direction.

2. Hearing the Doppler Effect Animation
ISNS Phenomena of Nature
Hearing the Doppler Effect Animation

3. Doppler Shift vs Velocity Animation
ISNS Phenomena of Nature
Doppler Shift vs Velocity Animation

4. ISNS 3371 - Phenomena of Nature
Sonic Boom
As the airplane moves, it pushes air molecules out of its way, continuously creating waves of compressed and uncompressed air. These air pressure waves move away from the airplane in all directions at the speed of sound.
Next, break the sound barrier by increasing the airplane's speed to supersonic - the air pressure waves (called shock waves) cannot precede the plane, and so accumulate in a cone behind the plane. The shock waves will move out and back from the plane, towards the ground. There is a sudden change in pressure when the shock wave hits your eardrum. You hear this as a loud sonic boom.

5. ISNS 3371 - Phenomena of Nature
There are actually two shocks - the first shock forms at the nose of the aircraft and the second near the tail - so you actually hear two sonic booms. They start out very close together (one body length apart, which means they are separated by much less than 0.1 sec), but, as they propagate the long distance to the Earth's surface, they spread apart, and the time between them gets as large as 1 sec. That's why you can actually hear two closely-spaced booms. The longer the aircraft's fuselage and the higher it is flying, the easier it is to distinguish the two shocks.
To increase the intensity of a sonic boom, increase the size of the airplane. The larger the aircraft, the more air it displaces and the stronger the shock waves become.

6. F/A-18 Hornet photographed just as it broke the sound barrier.
ISNS Phenomena of Nature
F/A-18 Hornet photographed just as it broke the sound barrier.
A leading theory is that a drop in air pressure at the plane described by the Prandtl-Glauert Singularity occurs so that moist air condenses there to form water droplets.

7. ISNS 3371 - Phenomena of Nature
Light

8. In space everyone can see you scream! (they just can’t hear you)
ISNS Phenomena of Nature
Light
What is light? - A vibration in an electromagnetic field through which energy is transported. Since it is an electromagnetic field, it does not require a medium -
In space everyone can see you scream! (they just can’t hear you)
The dual nature of light or wave-particle duality - light can be treated as a wave or as a particle:
Light as a wave
f  = c
Light as a particle
E = hf
photon

9. ISNS 4371 Phenomena of Nature
Dual Nature of Light
Light may show properties of a wave or of a particle, called a photon.
Newton (1680) explained light as a particle of energy. In reflection and refraction, light behaved as a particle.
Young, (circa. 1800) showed that light interfered with itself. Therefore, it must be a wave. Reflection and refraction could be explained by light being a wave.
Maxwell (1850) showed that light was a form of high frequency electromagnetic wave.

10. ISNS 4371 Phenomena of Nature
Dual Nature of Light
Einstein (1905) showed that in the photoelectric effect (light causing electrons to be emitted from a metal surface) light must act as a particle.
Planck (1900) developed a model that explained light as a quantization of energy. Energy of a light wave is present in bundles of energy called photons; the energy is said to be quantized into the photons.
Therefore, light must be regarded as having a dual nature; in some cases light acts as a wave; in others it acts like a particle.

11. The Photoelectric Effect
ISNS Phenomena of Nature
The Photoelectric Effect
First observed by Heinrich Hertz in light shining on a metal plate causes electrons to be knocked loose (ejected) from the metal plate.
Several aspects of the phenomena could not be explained in terms of an electromagnetic wave:
Increasing the brightness of the light did not eject faster electrons - think of light as a wave - brighter light (bigger amplitude wave) should eject more energetic (faster) electrons.
Energy and number of ejected electrons depends on color of light - for some metals, red light would not eject any electrons at all - blue lights ejects very fast electrons even if very dim.
The electrons were emitted immediately - no time lag - if light is dim, expect a delay while the waves wiggle the electrons and break them loose.

12. The Photoelectric Effect
ISNS Phenomena of Nature
The Photoelectric Effect
In 1905 Einstein gave a very simple interpretation of the results - the incoming radiation should be thought of as quanta of energy hf - a photon - with f the frequency.
- one of the crucial landmarks in the development of modern physics.
- introduced in one of his three papers, published in (called the Remarkable Year of Physics)
- helped to initiate the fundamental revolution in science that we now call Quantum Physics.
- it was for this work that he was awarded a Nobel Prize in not relativity!
Idea used in a number of technologies today including photovoltaic cells - solar cells.

13. Light as a Particle (Photon)
ISNS Phenomena of Nature
Light as a Particle (Photon)
Light propagates as quanta of energy called photons
Photons
move with speed of light
have no mass
are electrically neutral
Energy of a photon or electromagnetic wave:
E = hf = h c/ l
where
h = Planck’s constant
f = frequency of a light wave - number of crests passing a fixed point in 1 second
c = velocity of light
l = wavelength of a light wave -
distance between successive crests

14. ISNS 3371 - Phenomena of Nature
Light as a Wave
Remember: Light is a vibration in an electromagnetic field through which energy is transported.
So electrons can be manipulated by light. Electrons wiggle up and down as light passes by. It is a transverse wave - the vibration of particles is perpendicular to the propagation of the wave.

15. ELECTROMAGNETIC WAVES (LIGHT WAVES)
ISNS Phenomena of Nature
ELECTROMAGNETIC WAVES (LIGHT WAVES)
Velocity 186,000 miles/second
300,000 kilometers/second
3 x 106 m/second
• It takes 1 1/3 second for light to travel from the earth to the moon.
• It takes 8 1/3 minutes for light to travel from the sun to the earth.

16. Light Travel Time From Earth to the Moon our natural satellite
ISNS Phenomena of Nature
Light Travel Time
From Earth to the Moon
our natural satellite
1.25 seconds
From Earth to the Sun
the centre of our Solar System
8.3 min
From the Sun to Jupiter
the largest planet
41 min
From the Sun to Saturn
the furthest naked eye planet
85 min
From the Sun to Pluto
the furthest of the Sun's planets
5.5 hr
From the Sun to Alpha Centauri
the nearest star to us
4.3 yr
From the Sun to Sirius
the brightest star in our sky
8.6 yr
Distance where the Sun would no longer be visible to naked eye
60 yr
From the Sun to Polaris
the north pole star
650 yr
From the Sun to the Galactic centre
the centre of our Galaxy
31,000 yr
Galactic diameter
the diameter of our Galaxy
81,500 yr
To the Andromeda Galaxy
the nearest large galaxy
2,200,000 yr
Extinction of the dinosaurs
65,000,000 yr
To Q
typical quasar
4,500,000,000 yr
Formation of the Earth and Sun
4,700,000,000 yr
To remotest quasars
discovered in 1998
14,000,000,000 yr
Edge of Universe
limit of observable Universe
15,000,000,000 yr

17. ISNS 3371 - Phenomena of Nature
Light as a Wave
For a wave, its speed: s = f ( is wavelength)
But the speed of light is a constant, c.
For light: f  = c
The higher f is, the smaller  is, and vice versa.
Our eyes recognize f (or ) as color!

18. Visible Light Waves Animation
ISNS Phenomena of Nature
Visible light ranges through 7 major colors from long wavelengths (low frequency - red) to short wavelengths (high frequency - violet) - Red, orange, yellow, green, blue, indigo, violet (Roy G Biv)
Visible Light Waves Animation

19. The Electromagnetic Spectrum
ISNS Phenomena of Nature
The Electromagnetic Spectrum
Most wavelengths of light can not be seen by the human eye.
The visible part of the electromagnetic spectrum lies between ultraviolet and infrared light (between about 400 and 700 nm). The higher the frequency (shorter the wavelength), the higher the photon energy. Radio waves are at the long wavelength end of the spectrum and gamma rays are at the short wavelength end of the spectrum.

20. ISNS 3371 - Phenomena of Nature
Color
Additive primary colors - adding light of additive primary colors produces complementary colors - all colors produces white
Red Green Blue
Red + Green  Yellow
Red + Blue  Magenta
Green + Blue  Cyan
Red
Magenta
Yellow
Blue
Green
Cyan
White

21. ISNS 3371 - Phenomena of Nature
Color
Subtractive primary colors - mixing pigments (that absorb light) of various subtractive primary colors produce complementary colors - added all together, produce black.
Yellow Magenta Cyan
Yellow + Magenta  Red
Yellow + Cyan  Green
Magenta + Cyan  Blue

22. ISNS 3371 - Phenomena of Nature
Only four colors are used to print color illustrations and photos: (a) magenta, (b) yellow, (c) cyan, (e) black. (d) is with all but black, (f) is with all.

23. Four Ways in Which Light can Interact with Matter
ISNS Phenomena of Nature
emission – matter releases energy as light
absorption – matter takes energy from light
transmission – matter allows light to pass through it
reflection – matter repels light in another direction

24. ISNS 4371 Phenomena of Nature
Properties of Light
Law of Reflection - Angle of Incidence = Angle of reflection
Law of Refraction - Light beam is bent towards the normal when passing into a medium of higher Index of Refraction.
Light beam is bent away from the normal when passing into a medium of lower Index of Refraction.
Index of Refraction -
Inverse square law - Light intensity diminishes with square of distance from source.

25. ISNS 3371 - Phenomena of Nature
Mirror reflects light at angle equal to incoming angle -
Most materials reflect light randomly - scattering. Movie screen scatters light into array of beams that reaches every member of the audience

26. ISNS 3371 - Phenomena of Nature
Materials that transmit light are transparent
Materials that absorb light are opaque
In general - some combination of reflection, absorption, and transmission
Red glass transmits red light - absorbs all other colors
Green grass reflects green light - absorbs all other colors

27. Atmospheric Light Scattering
ISNS Phenomena of Nature
Atmospheric Light Scattering
Atmospheric gases are largely transparent to visible light
Most photons penetrate to the ground, warming it as the light is absorbed
Small portion of light is scattered
- why our sky is bright
- light is not scattered on Moon, Mercury
- their skies are dark - stars are visible during day
- shadows extremely dark
Gas molecules scatter blue light more effectively than red light

28. ISNS 3371 - Phenomena of Nature
Why is the Sky Blue?
Sunlight is scattered off the molecules of the atmosphere - called Rayleigh scattering - more effective at short wavelengths (the blue end of the visible spectrum). Little of the red, orange and yellow light is affected. Whichever direction you look, some of this scattered blue light reaches you. Since you see the blue light from everywhere overhead, the sky looks blue. As you look closer to the horizon, the sky appears much paler in color. To reach you, the scattered blue light must pass through more air. Some of it gets scattered away again in other directions. Less blue light reaches your eyes. The color of the sky near the horizon appears paler or white.

29. Why are Sunsets Red or Orange?
ISNS Phenomena of Nature
Why are Sunsets Red or Orange?
The blue light has been scattered out and away from the line of sight.
As the sun begins to set, the light must travel farther through the atmosphere before it gets to you. More of the light is reflected and scattered. As less reaches you directly, the sun appears less bright. The color of the sun itself appears to change, first to orange and then to red. This is because even more of the short wavelength blues and greens are now scattered. Only the longer wavelengths are left in the direct beam that reaches your eyes. Dust particles can scatter red and orange light in all directions leading to spectacular sunsets - why sunsets in LA are so beautiful - pollution.

30. ISNS 3371 - Phenomena of Nature
Moonrise
Earthrise
On the moon, there is no atmosphere to scatter light and the sky is black Atmosphere on Mars too thin to scatter light effectively - sky is reddish from presence in the atmosphere of reddish dust from surface. On Venus, almost all blue light scattered away - atmosphere dimly lit and appears reddish orange.