物理问题（Optics 和 EM）

剑侠

(1)a thin flake of mica(n=1.58) is used to cover 1 slit of a double-slit arrangement.The central point on the screen is occupied by what used to be the seventh bright fringe.If wavelength = 550nm, what is the thickness of the mica??

(2)two coherent radio point source seperated by 2m are radiating in phase with wavelength 0.50m. A detector moved in a circular path around the two sources in plane containing them will show how many maxima??

请大家帮帮忙了。这些全都是关于interference。因为这些问题是英文的，我不会翻译，请多多体谅。

[ 本帖最后由 剑侠 于 6-4-2007 09:36 PM 编辑 ]

剑侠

(1)The output of an AC generator is emf,E = Em sin wt , with Em = 25V and w = 377rad/s. It is connected to a 12.7H inductor.　(a)What is the maximum value of the current.　(b)When the current is maximum, what is the emf of the generator?　(c)is the generator supplying energy to or taking energy from the rest of the circuit??

(2)The radiation from a certain laser, although centered on 632.8 nm, has a finite "linewidth" of 0.10nm. Calculate the linewidth in frequency units.

(3)What inductance is required with a 17-pF capacitor in order to construct an oscillator capable of generating 550-nm electromagnetic waves?? Comment of your answer.

(4)Given an isolated conducting sphere of 13-cm radius. one wire carries a current of 1.0000020 A into it. another wire carries 1.0000000 A out of it. How long would it take for the sphere to increase in potential by 980 V??

(5)Light of wavelength 600nm is incident normally on a diffraction grating. Two adjacent principal maxima occur at sin@ = 0.20 and sin@ = 0.30. The fourth order is missing. (a)What is the seperation between adjacent slits?　(b)What is the smallest possible individual slit width?　(c)Name all the orders appearing on the screen with the values derived in (a) and (b)

请大家帮忙小弟解答这些问题。谢谢。

剑侠

怎么没人回答我？？？？

这里还有2题关于optics

(1) Give the doppler wavelength shift if any for the sodium D2 line (589.00nm) emitted from a source moving in a circle with constant speed 0.122c as measured by an observer fixed at the centre of the circle.
答案是4.43nm 。但是，我做到 4.58nm 。

(2) A source of radio waves, rest frequency 188MHz, is moving at a speed of 0.717c transverse to the line of sight to a detector. At what angle to the line of sight must a second source, rest frequency 162MHz, move also at 0.717c if the frequencies of the 2 source as received at the detector are to be equal.
答案是78.9度。但是，这题我做到34.9度 。

请大家帮我解答这些问题。谢谢。

noman

你问的问题都是关于electromagnetic waves的！不是每个人都懂的啊！这是我一年前读的subject。要帮你解答可要翻回之前的notes。里面还有一大堆的formulas和equations。

现在我在忙FYP和final exam，暂时帮不到你。

剑侠

ocean waves moving at a speed of 4m/s are approaching a beach at an angle of 30 degrees to the normal. When the depth of the ocean changes, the speed drops to 3m/s. What is the angle between the direction of wave motion and the normal close to the beach.(assume the law of refraction as for light). Explain why most waves come in normal to the shore even though at large distances they approach at a variety of angles.

这题它的index of refraction是什么？？？？请大家帮我解答这题。谢谢。

[ 本帖最后由 剑侠 于 15-4-2007 09:34 PM 编辑 ]

剑侠

请大家回答我的问题，在下感激不尽。

微中子

原帖由 剑侠 于 15-4-2007 09:33 PM 发表
ocean waves moving at a speed of 4m/s are approaching a beach at an angle of 30 degrees to the normal. When the depth of the ocean changes, the speed drops to 3m/s. What is the angle between the  ...

这里,可以用index of refraction = v1/v2这个方程式。

原帖由 剑侠 于 6-4-2007 09:48 PM 发表
(1) Give the doppler wavelength shift if any for the sodium D2 line (589.00nm) emitted from a source moving in a circle with constant speed 0.122c as measured by an observer fixed at the centre of the circle.
答案是4.43nm 。但是，我做到 4.58nm 。

(2) A source of radio waves, rest frequency 188MHz, is moving at a speed of 0.717c transverse to the line of sight to a detector. At what angle to the line of sight must a second source, rest frequency 162MHz, move also at 0.717c if the frequencies of the 2 source as received at the detector are to be equal.

这里你用什么方法来算？应该是属于特殊相对论的问题。(1)可以把它看成是time dilation.(2)懒惰算，不过应该可以用relativistic doppler shift 来解吧？

其他的有空再看看。

剑侠

什么时候要用optical path length????

有时侯直接用length有时侯却用optical path length？？？