科目近代物理编著秦立原本powerpoint教学档案内课件

1、 科目:近代物理 編著:秦立原 本power point教學檔案內容，乃教師本人根據 Arthur Beiser之Concepts of modern Physics原著演繹並解讀而成。請尊重智財權，勿任意下載流通。 Modern PhysicsSpecial relativityParticle characteristics of wave Modern PhysicsSpecial relativiSpecial RelativitySec. 1.1: All motion is relative; the speed of light in free space is the same

2、 for all observers. remark:(1)The above two statements have no dependence, the first is not the cause of the second and the second is not the cause of the first. (2)All motion is relative means that, when we say something A is in motion, the motion must relative to something B). And B is also in mot

3、ion to A ,this is just the thing the first statement want to express. (3)Observers in the second statement represents inertial frames of reference. An inertial frame of reference is one which Newtons first law of motion holds. Any frame of reference that moves at constant velocity relative to an ine

4、rtial frame is itself an inertial frameSpecial RelativitySec. 1.1: Al(4)The word free space in the second statement is very important. The speed of light in free space is 2.998108m/s for all inertial frames of reference.(4)The word free space in thPostulates of Special RelativityPostulate 1:The laws

5、 of physics are the same in all inertial frames of reference. Remark: So called the laws of physics includes: (p15., Eisberg)(1)Electromagnetic phenomena (including the fact that the propagation velocity of light is equal to the constant value c)(2)The laws of mechanics: Fig.1.6 discuss this postula

6、te. In that fig., the speed of a spacecraft relative the earth is assumed to be v and v is greater than c (light speed in free space). A man in the spacecraft switches on a flashlight to the front of the spacecraft and he would see the flashlight illuminates the front wall of the craft. Postulates o

7、f Special RelativiHowever, the observer on the earth would see the flashlightilluminates the back wall of the craft, because vc in theearth frame of reference. Now, the flashlight is seen to illuminates different parts of the craft bydifferent frames. It is just the different results which conflict

8、with the postulate one.So we know the assumption that v, the speed of any spacecraft must not greater than the constant c. And we can conclude that the speed of nothing can greater than the constant cHowever, the observer on the ePostulate 2: The speed of light in free spacehas the same valuein all

9、inertial frames of reference. Unlike postulate 1which is based on pure thinking and life experience, postulate 2 is based on the resultes of many experiments. Fig1.1illustrates postulate 2. Jack is in the earth, Lee in a spacecraft. When the craft pass him with v=(2/3)c, Jack turn on a searchinhligh

10、t. Jack will surely find the speed of the searchinglight is c.However, Lee will find the speed of the searchinglight is also c, but not (1- 2/3)c. Postulate 2: The speed of lighParticle properties of wavesIn classical physics,particles and waves are separate components of physical reality. The mecha

11、nics of particles and the optics of waves are traditionally independent disciplines. They both have thtir own serious experiments and principles correspond those experiments. However, we find that a moving particle,such as an electron, can be seen as a wave.Simiarly, under some cases,electromagnetic

12、 waves behave as if they consists of streams of particles. Then we can see an EM wave as a particle.Together with special relativity,the wave-particle duality is the central of modern physics. Particle properties of wavesInIn 1864, Maxwell suggested that accelerated charges generate linked electric

13、and magnetic disturbances that can travel infinitely through space.If the above mentioned charges oscillate periodically, disturbnaces will becomes waves, and E,B,v will prependicular to each other, where v is the propergation velocity vector of EM waves.Before the suggestion was proposed by Maxwll,

14、 people only knew the Faradys induction law: A changing magnetic field can induce a current in a wire loop.Maxwell proposed the converse: a changing electric field has a changing magnetic field associated with it. In 1864, Maxwell suggested thaThe product of electric permittivity and magnetic permea

15、bility is derived to be equal to the inverse of c2, it cant be just an accident. So Maxwell again suggested that light consists of EM waves.During Maxwells lifetime, No experiments found the existence of EM waves.In 1888, Heinrich Hertzs experiment showed the existence of EM waves. He found the EM w

16、aves could be reflected,refracted, and diffracted.The product of electric permitBlackbody radiationsWhen discussing blackbody radiations, radiations are not reflections. They are the nature ability of matters, the higher the surrounding temperature is, the stronger the radiations are.Why did scienti

17、st be interested in blackbody? The answer is the reflection ratios of different matters are also different. It effects the detecting of radiations. If scientist could exclude the existence of reflections, they would be able to see all the collected light as pure radiations without any reflections. S

18、o that scientist can concentrate their attention on the relation between the intensity of radiations and temperature. The ability of a body to radiate is proportional to its ability to absorb radiation. Blackbody radiationsWhen discuIn blackbody spectra. The spectral distribution of energy in the ra

19、diation depends only on the temperature. The higher the temperature, the greater the amount of radiation and the higher the frequency at which the maximum emission occurs.Rayleigh and Jeans considered the radiation inside a cavity of absolute temperature T whose walls are perfect reflectors to be a

20、series of standing em waves. They also combined the formulas of the standing waves density and classical average energy per standing wave.So Rayleigh and Jeans derived (2.3)In blackbody spectra. The specPlanks treatment for blackbody radiationPlanks treatment for blackbod(2.6) is also the average en

21、ergy of the standing waves with the fixed frequency in the cavity. For those standing waves with greater . This average energy will be smaller so that cancel the effect of G() for the greater . Example (2.1) talk about the evidence of quantum effect. The energy of a quantum, h , is 10-29 times of n

22、h ,0.04J, the total energy of the fork. 10-29 times is so small that we say the evidence of the quantum effect is very small (But we cant say there is no quantum effect ). If we want to increase the evidence of quantum effect, we should decrease the value of n very rapidly. If its value (1029) can b

23、e decreased to smaller than 10, we should be able to say the quantum effect is evident. But the strike force to the fork cannot be decreased to so small a value (Remember that the value of the fork is 0.04J, Its uneasy to make it become 0.04 10-28 0.04 10-29 )(2.6) is also the average ener 例(3.1a)中g

24、olf ball 非oscillator，故欲論其能量量化明顯與否時，必須先令其能量可以量化。故須令golf ball 侷限於箱中運動。而此例中ball 活動空間並未受 侷限，故只能討論其波動行為之明顯性。此例中之golf ball 雖波長太小而不易發現其波動行為；但因與例b中 之electron均具明確之波長故=0, s.t. p=0，使x=(由測不準原理) 。故在運動方向上各處均可出 現，而並未被侷限住(例3.5中之marble就被侷限住了，故p0，s.t. 0且能量被量化) 例(3.1a)中golf ball 非oscillato科目近代物理编著秦立原本powerpoint教学档案内课件原子核的尺寸最靠近的距離Chin:(1)此值係指動