Presentation on theme: "ISNS Phenomena of Nature"— Presentation transcript:
1ISNS 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.
2Hearing the Doppler Effect Animation ISNS Phenomena of NatureHearing the Doppler Effect Animation
3Doppler Shift vs Velocity Animation ISNS Phenomena of NatureDoppler Shift vs Velocity Animation
4ISNS 3371 - Phenomena of Nature Sonic BoomAs 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.
5ISNS 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.
6F/A-18 Hornet photographed just as it broke the sound barrier. ISNS Phenomena of NatureF/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.
8In space everyone can see you scream! (they just can’t hear you) ISNS Phenomena of NatureLightWhat 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 wavef = cLight as a particleE = hfphoton
9ISNS 4371 Phenomena of Nature Dual Nature of LightLight 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.
10ISNS 4371 Phenomena of Nature Dual Nature of LightEinstein (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.
11The Photoelectric Effect ISNS Phenomena of NatureThe Photoelectric EffectFirst 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.
12The Photoelectric Effect ISNS Phenomena of NatureThe Photoelectric EffectIn 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.
13Light as a Particle (Photon) ISNS Phenomena of NatureLight as a Particle (Photon)Light propagates as quanta of energy called photonsPhotonsmove with speed of lighthave no massare electrically neutralEnergy of a photon or electromagnetic wave:E = hf = h c/ lwhereh = Planck’s constantf = frequency of a light wave - number of crests passing a fixed point in 1 secondc = velocity of lightl = wavelength of a light wave -distance between successive crests
14ISNS 3371 - Phenomena of Nature Light as a WaveRemember: 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.
15ELECTROMAGNETIC WAVES (LIGHT WAVES) ISNS Phenomena of NatureELECTROMAGNETIC WAVES (LIGHT WAVES)Velocity 186,000 miles/second300,000 kilometers/second3 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.
16Light Travel Time From Earth to the Moon our natural satellite ISNS Phenomena of NatureLight Travel TimeFrom Earth to the Moonour natural satellite1.25 secondsFrom Earth to the Sunthe centre of our Solar System8.3 minFrom the Sun to Jupiterthe largest planet41 minFrom the Sun to Saturnthe furthest naked eye planet85 minFrom the Sun to Plutothe furthest of the Sun's planets5.5 hrFrom the Sun to Alpha Centaurithe nearest star to us4.3 yrFrom the Sun to Siriusthe brightest star in our sky8.6 yrDistance where the Sun would no longer be visible to naked eye60 yrFrom the Sun to Polaristhe north pole star650 yrFrom the Sun to the Galactic centrethe centre of our Galaxy31,000 yrGalactic diameterthe diameter of our Galaxy81,500 yrTo the Andromeda Galaxythe nearest large galaxy2,200,000 yrExtinction of the dinosaurs65,000,000 yrTo Qtypical quasar4,500,000,000 yrFormation of the Earth and Sun4,700,000,000 yrTo remotest quasarsdiscovered in 199814,000,000,000 yrEdge of Universelimit of observable Universe15,000,000,000 yr
17ISNS 3371 - Phenomena of Nature Light as a WaveFor a wave, its speed: s = f ( is wavelength)But the speed of light is a constant, c.For light: f = cThe higher f is, the smaller is, and vice versa.Our eyes recognize f (or ) as color!
18Visible Light Waves Animation ISNS Phenomena of NatureVisible 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
19The Electromagnetic Spectrum ISNS Phenomena of NatureThe Electromagnetic SpectrumMost 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.
20ISNS 3371 - Phenomena of Nature ColorAdditive primary colors - adding light of additive primary colors produces complementary colors - all colors produces whiteRed Green BlueRed + Green YellowRed + Blue MagentaGreen + Blue CyanRedMagentaYellowBlueGreenCyanWhite
21ISNS 3371 - Phenomena of Nature ColorSubtractive primary colors - mixing pigments (that absorb light) of various subtractive primary colors produce complementary colors - added all together, produce black.Yellow Magenta CyanYellow + Magenta RedYellow + Cyan GreenMagenta + Cyan Blue
22ISNS 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.
23Four Ways in Which Light can Interact with Matter ISNS Phenomena of Natureemission – matter releases energy as lightabsorption – matter takes energy from lighttransmission – matter allows light to pass through itreflection – matter repels light in another direction
24ISNS 4371 Phenomena of Nature Properties of LightLaw of Reflection - Angle of Incidence = Angle of reflectionLaw 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.
25ISNS 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
26ISNS 3371 - Phenomena of Nature Materials that transmit light are transparentMaterials that absorb light are opaqueIn general - some combination of reflection, absorption, and transmissionRed glass transmits red light - absorbs all other colorsGreen grass reflects green light - absorbs all other colors
27Atmospheric Light Scattering ISNS Phenomena of NatureAtmospheric Light ScatteringAtmospheric gases are largely transparent to visible lightMost photons penetrate to the ground, warming it as the light is absorbedSmall 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 darkGas molecules scatter blue light more effectively than red light
28ISNS 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.
29Why are Sunsets Red or Orange? ISNS Phenomena of NatureWhy 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.
30ISNS 3371 - Phenomena of Nature MoonriseEarthriseOn 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.